Use of a dual bakeable polyester film in thermoformed packaging applications and dual bakeable thermoformed packages obtained therefrom

文档序号：1539051 发布日期：2020-02-14 浏览：9次中文

阅读说明：本技术 可双法烘烤的聚酯膜在热成型包装应用中的用途和由其获得的可双法烘烤的热成型包装 (Use of a dual bakeable polyester film in thermoformed packaging applications and dual bakeable thermoformed packages obtained therefrom ) 是由 A.利派罗蒂 M.西奥卡 S.迪菲奥里 B.朱斯蒂 R.佛尔罗尼于 2018-06-27 设计创作，主要内容包括：本发明涉及热成型食品包装方法和适合在微波炉、传统烤箱和对流烤箱中直接烹调包装中的食品的可双法烘烤的热成型食品包装。这些包装的特征在于良好的气密性、干净的可剥离性、自排气、非常好的光学特性,并且如果被收缩,则具有非常吸引人的外观。(The present invention relates to a method of packaging thermoformed food products and to dual ovenable thermoformed food packages suitable for direct cooking of the food product in the package in microwave ovens, conventional ovens and convection ovens. These packages are characterized by good air tightness, clean peelability, self-venting, very good optical properties and, if shrunk, a very attractive appearance.)

1. A thermoformed food packaging process for making a dual ovenable thermoformed package comprising

Providing a thermoformable, dual bakeable biaxially oriented polyester film as a base web,

-forming the bottom web so as to provide at least cavities having openings;

-placing a food product in the cavity through the opening;

-closing the cavity at the opening by hermetically sealing the bottom web to itself or by providing a dual ovenable top web and hermetically sealing the dual ovenable top web to the bottom web around the opening; and

-cutting out the sealed packages,

characterized in that the film of the bottom web comprises:

an outer heat sealable polyester layer a),

an inner polyester base layer b) comprising a polyester having an Intrinsic Viscosity (IV) higher than 0.75 dl/g measured according to ASTM D4603-03,

an outer polyester layer c), and

i) the bottom web is formed with a stretch ratio higher than 1.26, or

ii) the film of the bottom web is heat-shrinkable, and the sealed package is finally heat-shrunk.

2. The packaging process of claim 1 wherein i) the bottom web is formed at a stretch ratio above 1.26 and ii) the film of the bottom web is heat shrinkable and the sealed package is finally heat shrunk.

3. The packaging process of claim 1 or 2 wherein the film of the bottom web consists of an outer heat sealable polyester layer a), an inner polyester base layer b) comprising a polyester having an Intrinsic Viscosity (IV) higher than 0.75 dl/g measured according to ASTM D4603-03, and an outer polyester layer c).

4. The packaging method of any one of the preceding claims, wherein the step of closing the cavity at the opening is performed under vacuum.

5. The packaging method according to any one of the preceding claims, wherein the total thickness of the film before thermoforming is less than 50 microns, preferably less than 40 microns, more preferably less than 35 microns, 30 microns or 25 microns.

6. The packaging process according to any one of the preceding claims, wherein the thermoformed food packaging process is a deep-drawing packaging process, wherein the draw ratio is higher than 2.0, preferably higher than 2.5, 3.0, 3.5, 4.0 or 4.5.

7. The packaging process of any preceding claim wherein the process is a thermoforming-shrink packaging process wherein the film of the bottom web has a percent free shrink in at least one of the LD or TD direction of at least 3%, more preferably at least 4%, measured according to the test method reported in this specification prior to thermoforming.

8. The packaging process of any preceding claim wherein the process is a thermoforming-shrink packaging process wherein the film of the bottom web has a total free shrink percentage of at least 5%, more preferably at least 10%, measured according to the test method reported in the present specification before thermoforming.

9. The packaging method of any of the preceding claims wherein the film of the bottom web is further characterized by

-a tensile strength in at least one of the LD or TD direction of at least 1500 Kg/cm²More preferably at least 1600Kg/cm²And/or

-elongation at break in at least one of LD or TD direction of at least 100%, more preferably at least 105%, and/or

-a modulus of elasticity in at least one of the LD or TD direction of at least 20,000 Kg/cm²More preferably at least 22,000 Kg/cm²All of these properties were measured at 23 ℃ according to ASTM D882.

10. The packaging method of any preceding claim, wherein the biaxially oriented film of the bottom web is simultaneously oriented in the LD and TD directions.

11. The packaging process of any preceding claim wherein the polyester of the base layer b) of the film of the bottom web has an Intrinsic Viscosity (IV) of at least 0.8 dl/g.

12. The packaging method of any one of the preceding claims, wherein the film of the bottom web comprises

A heat-sealable layer a) comprising

About 25 to 70 weight percent of at least a first amorphous polyester having a melting temperature not higher than the melting temperature of the polyester of the base layer b),

10 to 20 weight percent of at least a thermoplastic resin selected from the group consisting of polyamides, polystyrenes, polyethylenes, ionomers, ethylene/unsaturated carboxylic acid copolymers, ethylene/unsaturated ester copolymers, ethylene/propylene copolymers, maleic anhydride modified polyethylenes, and ethylene/cyclic olefin copolymers, preferably maleic anhydride modified polyethylenes, and

20 to 60 wt% of at least another polyester characterized by an intrinsic viscosity of at least 0.75 dl/g or higher and/or by a glass transition temperature Tg not higher than 80 ℃ and/or a melting point higher than 240 ℃, measured according to ASTM D3418; and/or

-an inner polyester substrate b) comprising a mixture of at least 50% of a polyester resin having an intrinsic viscosity higher than 0.75 dl/g and at most 50% of an amorphous polyester; and/or

-an outer polyester layer c) comprising a polyester characterized by an intrinsic viscosity of at least 0.75 dl/g or higher and/or by a glass transition temperature Tg not higher than 80 ℃ and/or a melting point higher than 240 ℃, measured according to astm d 3418.

13. The packaging method of any of the preceding claims, wherein the film of the bottom web consists of

A heat-sealable layer a) comprising

About 25 to 70 weight percent of at least a first amorphous polyester having a melting temperature not higher than the melting temperature of the polyester of the base layer b),

-an inner polyester substrate b) comprising a mixture of at least 50% of a polyester resin having an intrinsic viscosity higher than 0.75 dl/g and at most 50% of an amorphous polyester; and

14. The packaging method of any of the preceding claims, wherein the film of the bottom web consists of

-a heat-sealable layer a) consisting of:

about 40 to 70 weight percent of at least a first amorphous polyester having a melting temperature not higher than the melting temperature of the polyester of the base layer b),

10 to 20% by weight of at least a thermoplastic resin selected from the group consisting of ethylene/unsaturated carboxylic acid copolymer, ethylene/unsaturated ester copolymer and maleic anhydride modified polyethylene, and

20 to 50 wt% of at least one other polyester characterized by an intrinsic viscosity of at least 0.75 dl/g or higher and/or by a glass transition temperature Tg not higher than 80 ℃ and/or a melting point higher than 240 ℃; and

-an inner polyester substrate b) consisting of a mixture of at least 55% of a polyester resin having an intrinsic viscosity higher than 0.75 dl/g and at most 45% of an amorphous polyester; and

-an outer polyester layer c) comprising at least 95% of the same polyester as the base layer b), characterized by an intrinsic viscosity of at least 0.75 dl/g.

15. The packaging process according to any one of the preceding claims, wherein, in the film of the bottom web, the same amorphous polyester of the base layer b) comprising the heat-sealable layer a) and/or the polyester of the outer polyester layer c) is the same polyester of the base layer b), having an intrinsic viscosity higher than 0.75 dl/g.

16. The packaging method of any of the preceding claims, wherein the film of the bottom web is a coextruded film.

17. A dual bakeable thermoformed flexible container made by thermoforming a film of the bottom web of any of the preceding claims, the container comprising a thermoformed cavity and an opening, wherein the thermoformed cavity is greater than 1 cm deep or the thermoformed container is heat shrinkable.

18. The flexible container of claim 17 wherein the thermoformed cavity has a depth of greater than 1 cm and the thermoformed container is heat shrinkable.

19. The flexible container according to claim 17 or 18, wherein the stretch ratio of the thermoformed container is higher than 1.26, preferably higher than 2.0, more preferably higher than 2.5.

20. The flexible container of claims 17 to 19 wherein the thermoformed cavity has a depth of greater than 2 cm, preferably greater than 3 cm or 4 cm.

21. The flexible container of claims 17 to 20 wherein the thermoformed film has a total percent free shrink after thermoforming of at least 40%, more preferably at least 45% or 50%, measured according to the test method reported in the present specification.

22. The flexible container of any one of claims 17 to 21 wherein the container further comprises a flange surrounding the opening, the flange adapted to be sealed to a dual ovenable top web.

23. A dual ovenable, air tight thermoformed package comprising

A dual ovenable thermoformable flexible container of any one of claims 17 to 22, comprising a thermoformed cavity and an opening,

a food item to be placed in the cavity,

the opening is hermetically closed by a flexible container that is self-sealing at the opening or by a dual bakeable top web sealed to the container around the opening.

24. The package of claim 23 which is a vacuum package.

25. The package of claim 23 or 24 wherein at least the flexible container is heat shrunk.

26. The package of any of claims 23 to 25 wherein a top web is present and the top web is heat shrunk.

27. The package of any of claims 23 to 26 wherein the flexible container and the top web are made from the same film.

28. The package of any of claims 23 to 27 wherein the top web is also thermoformed.

29. The package of any one of claims 23 to 28 wherein the food product is selected from the group consisting of fish, meat, processed meat, poultry, pork, lamb, baked goods, seafood, stabilized vegetables or ready meals.

30. A method for cooking a food product comprising

-providing a dual ovenable thermoformed package according to any of claims 23 to 29 which hermetically closes the food product, and

-cooking the packaged food product in the package in a microwave or in a conventional oven.

31. The method of claim 30, wherein the cooking step is performed in a conventional oven at a temperature above 205 ℃ and/or up to 220 ℃.

Technical Field

The present invention relates to the use of oriented polyester films in thermoforming food packaging processes, in particular in deep-drawing and thermoforming-shrinking food packaging processes. Furthermore, the present invention relates to a dual ovenable thermoformed package, in particular a dual ovenable thermoformed food package for cooking with the package.

Background

Packaged cook-in packages, i.e. packages in which the food product can be directly cooked in the package, in a microwave oven or a conventional oven, in boiling water or water vapor, are becoming more and more popular as it reduces the time spent in preparing meals, is effective, does not require cooking skills and allows for better portion control.

In addition, if cooking is done in a complete package, the cooking time is generally reduced, the oven remains clean, does not release unpleasant odors, and maintains the flavor of the product.

In certain applications, such as in cooking fresh fish products, packaged cooking methods are particularly desirable because they avoid handling raw fish and reduce the risk of contamination. Few plastic materials are suitable for the most desirable dual ovenable belt packaging cooking applications, namely the following materials:

microwave transparent for cooking in a microwave oven (microwave heatable),

resistant to temperatures higher than 205 ℃ and up to 220 ℃ for high-temperature cooking (bakable) in a conventional oven,

being sufficiently strong to prevent leakage from the package during storage and transport, but at the same time being easily peelable to open smoothly, and self-venting to allow steam to escape from the package during cooking,

capable of providing a core temperature for the food that is high enough to kill pathogens and bacteria throughout the cooking process,

transparent and non-whitening during cooking to allow inspection,

approved by regulatory agencies for food contact use, i.e. without release of contaminants throughout the processing cycle including any pre-cooking, packaging, heat sealing, storage and cooking steps.

Materials which have been developed in large part in practice and are used for producing bakeable packaging in the two-process are predominantly based on polyester.

In the prior art documents, bi-ovenable packages such as disclosed in WO2007093495, WO2009013284 and WO2012160142 in the name of Cryovac or available on the market generally comprise a plastic tray closed with a heat-shrinkable polyester film oriented with a lid sealed around the flange of the tray (a bi-ovenable tray lidded package).

Other dual ovenable packages may include bags or pouches that enclose a food product, where the bags or pouches are pre-manufactured according to conventional bag manufacturing processes or are manufactured in-line in a form-fill-seal process from a dual ovenable polyester film.

Additional dual ovenable packages may include thermoformed flexible containers (e.g., pouches) having an opening, the containers being made from a dual ovenable polyester film by thermoforming, which encapsulates the food product and is closed by self-sealing the same film at the opening or by sealing a flexible dual ovenable lid around the opening.

Thermoforming is a manufacturing process in which a plastic film is heated to a forming temperature, formed into a specific shape in a mold, cooled and trimmed to produce containers, lids, trays, blisters and other products for food, medical and general packaging applications.

Thermoforming is widely used for packaging of food products due to process flexibility, packaging speed and ease of automation.

Thermoformed containers, such as pouches or trays, can be pre-manufactured prior to the packaging process or manufactured in-line in a continuous manner in a thermoformed packaging process.

Typically, in a continuous thermoforming packaging process for high volume, thin gauge products, a plastic film (bottom web) is fed from a roll into an oven for heating to forming temperature. The heated film is then fed to a forming station where the mold and pressure chamber are closed over the film.

Vacuum is then applied to remove the trapped air and draw the material into or onto the mold along with the pressurized air to form the plastic into the fine shape of the mold, thereby forming a plurality of concave containers. Once the containers are formed from the bottom web, the products to be packaged are loaded in the containers, air is evacuated from the inside, and the package can then be closed by heat-sealing the upper peripheral portion of each container with a lid (top web), which can be, for example, a non-thermoformed film, another thermoformed flexible container, or a stretched film, to produce a plurality of vacuum-packaged products in a continuous manner.

The continuous web comprising the closed packages is then conveyed to a cutting station, where a die cuts the packages from the remaining web.

The remaining web is usually wound onto a take-up reel or fed to an in-line granulator for recirculation.

"deep drawing" is a particularly desirable thermoforming application, named for the rather high final depth of formed containers for forming trays, pouches and similar products.

Films for deep drawing must have several properties suitable for use.

First, because the material is subjected to much higher stretching than that of conventional thermoforming, it must be given exceptionally high formability.

In fact, in thermoforming deep cavities, the flat sheet defining the surface must be able to provide a much higher surface of the cavity. When the sheet is heated and pressed into a deep mold, it undergoes significant stretching to conform to the cavity shape. As the sheet is stretched, it thins and may break.

In addition, the film must conform closely to all the details of the mold, maintaining high definition. At the same time, the thermoformed film should not produce the so-called "set back" effect, i.e. the shaped container should retain as much as possible the shape and dimensions given by the mould when it is removed from the mould.

The film must also have good mechanical properties so that the final package, in which the thickness of the packaging material is reduced by the forming step, still has the necessary resistance to mechanical damage.

Known films for deep drawing are generally characterized by the presence of a reinforcing layer, preferably a polyamide layer, such as the laminate shown in WO2005/063483 in the name of Du Pont. These laminates are not suitable for dual process bakeable applications.

WO2012027043a1 in the name of Cryovac also discloses a thermoforming process wherein the thermoformed film is a polyamide based film.

The resulting package according to the definition given therein (page 1, lines 17-23) will be subjected to conventional heating by exposure to temperatures of 375 ° f or 400 ° f (i.e., 190 ℃ or 204 ℃) in a microwave and oven. However, due to the presence of lower melting point resins, especially in the outer abuse layer of the film, they would not be suitable for cooking in an oven at temperatures above 205 ℃ and up to 220 ℃.

A variant of the thermoforming packaging process commonly used for food packaging is the so-called thermoforming-shrink or roll-up-shrink packaging process. In this application, a thermoplastic heat shrinkable film unwound from a roll is thermoformed in-line, loaded with product, closed, and then heat shrunk around the product.

Thermoforming-shrink-wrapping processes generally involve:

-heating the bottom web and forcing it into the shape of the mould by means of positive or negative air pressure;

-placing the food product to be packaged in the formed web;

-applying a vacuum and heat sealing the top web to the bottom web so that the package is completely sealed, and finally

-heat shrinking the package to obtain a better and more attractive appearance.

The top web may be heat shrinkable or non-heat shrinkable.

The shrinkage of the packaging material of the bottom web, the top web or both the bottom and top webs caused by the heat treatment provides the desired tight appearance for the final vacuum package. Examples of such packages are for example the packages described in EP2030784 in the name of Cryovac, US8424273 in the name of CSF, US2008/0152772, and US20050173289 in the name of Multivac. The multilayer heat shrinkable films used therein are not polyester based and are not suitable for dual process bakeable applications.

In thermoforming-shrinking applications, it is required that the film has optimal shrink properties, not only before thermoforming, but especially after thermoforming, in order to obtain tight packaging.

Thus, once thermoformed, the film must maintain some free heat shrinkage and some shrink tension in the LD and TD directions to ensure that the package appearance is as tight as desired after the shrinking step.

In addition, the film should have good optical properties after stretching and shrinking, not only for purely aesthetic reasons, but also to allow visual inspection of the packaged product.

There are packaging methods known in the literature and recently applied in the food industry which combine deep drawing followed by shrinking, i.e. which comprise a deep-drawn oriented heat shrinkable film to form a flexible shrinkable container with a deep cavity.

These deep draw thermoforming-shrink wrapping processes differ from conventional deep draw processes in that a heat-shrinkable flexible film is used in place of the standard non-heat-shrinkable, generally thicker laminate. The main advantages provided by deep draw thermoformed shrink packaging with heat shrinkable film are a reduction in the amount of packaging material used and an improvement in the packaging appearance which makes the product more appealing.

Standard dual bakeable oriented PET materials, which are typically used as lids for tray closures or as non-thermoformed pouches, are not suitable as a forming web in thermoforming, especially in deep drawing, because they are endowed with insufficient formability. Furthermore, they are also not suitable for shrink applications because they have very poor shrink properties.

To the best of the applicant's knowledge, there are few examples of using a dual bakeable polyester film in standard (i.e., shallow) thermoformed packages for dual bakeable applications.

For example, document WO2015/189351 in the name of Cryovac discloses the use of polyester films in packaging perishable food (e.g., fish) under modified atmosphere to increase the shelf life of the product and allow for belt-packaged cooking in the same package. A possible package comprises a top polyester film and a bottom polyester film sealed together and enclosing the food product. The bottom polyester film may be thermoformed. In the examples, carrier film 1 (which is heat-set and no longer shrinkable) was molded to a maximum depth of 1 cm (see examples 5 and 6 for stretch ratios of 1.24 and 1.26, respectively). The packages of these embodiments do not include any product and do not shrink.

Document WO2006/002263 in the name of DuPont describes thermoformed pouches for band-packaged cooking applications made from polyester-polyamide films comprising specific sulfur-containing polyesters under standard thermoforming conditions.

To the best of the applicant's knowledge, even fewer examples of the use of polyester films in deep-drawn food packaging for dual-ovenable applications.

Document WO2007/054698 in the name of Du Pont describes a method of packaging fish or meat comprising thermoforming a thermoformable polyester receptor film that is bakeable to provide a cavity, placing the product in the cavity, and closing the package with a two-way bakeable cover film by heat sealing the two films around the product.

The intrinsic viscosity of the copolyester used in the thermoformable film is lower than 0.75 dl/g (see pages 20-21 of the description).

In examples 1-4, the double bakeable polyester films of unknown composition (designated Mylar P25, HFF-FT3, and HFF-FT7, respectively) were stretched to a depth of 50 mm. These examples do not provide information about the shape, size of the mold and about the draw ratio. The final package is not subjected to heat shrinking.

These films had less formability than the films obtained in comparative example 1 of the present specification, compared to the films of the present invention.

Furthermore, according to the Table of Mylar P25 specifications, the films exhibited a percent free shrink at 150 ℃ of 2.5% along LD and 1.5% along TD (ASTM E794), which would not be ideal for thermoforming-shrink packaging applications. Thus, as shown in this example 4, the commercial film designated Mylar @ OL25 performed less well in thermoforming-shrink applications, producing a wrinkled shrink wrap (FIG. 5B).

US20050074598 describes coextruded biaxially oriented polyester films for tray closures comprising a base layer (B) and a heat-sealable top layer (a), these films being characterized by a specific composition of layer (a) which imparts heat-sealability and peelability when sealed to APET/CPET trays. The document does not disclose the use of these films in any thermoforming application. To the best of the applicant's knowledge, there is no example of using polyester film in the thermoforming-shrink wrapping process for two-process bakeable applications.

In summary, there remains a need for a dual bakeable highly formable polyester film suitable for deep draw and/or thermoforming-shrink packaging, i.e. a dual bakeable film that shapes well in thermoforming and withstands high draw ratios, does not retract upon demolding from a mold, and, when heat shrinkable, is highly shrinkable after thermoforming, thus providing a very tight attractive shrink package.

Brief description of the invention

The applicant has surprisingly found that the known dual bake polyester film disclosed in document WO2012/160142 for use as a lid in tray closures and the known dual bake polyester film disclosed in WO2015/189351 as a non-thermoformed or lightly thermoformed non-shrinkable container perform very well in thermoformed packaging applications such as deep draw and thermoformed-shrink packaging.

The applicant has found that these films are characterized by unexpectedly high formability, allowing deep drawing even at thicknesses lower than conventional films. Advantageously, the use of thinner films results in cost savings and improved carbon footprint.

In addition, these films in their heat-shrinkable form (i.e., when not heat-set) exhibit surprisingly high shrinkage after thermoforming, thus providing very tight packaging after shrinking. This is surprising because formability and shrinkage are generally inversely related.

Finally, due to their remarkable heat resistance, these films can provide deep-drawn and/or shrink packaging which is dual bakeable even at temperatures above 205 ℃ and up to 220 ℃, which is particularly popular for certain packaged cooking applications.

Accordingly, a first object of the present invention is a thermoformed food packaging process for making a dual ovenable thermoformed package comprising

Providing a thermoformable, dual bakeable biaxially oriented polyester film as a base web,

-forming the bottom web so as to provide at least cavities having openings;

-placing a food product in the cavity through the opening;

-cutting out the sealed packages,

characterized in that the bottom web comprises:

an outer heat sealable polyester layer a),

an inner polyester base layer b) comprising a polyester having an Intrinsic Viscosity (IV) higher than 0.75 dl/g measured according to ASTM D4603-03,

an outer polyester layer c), and

i) the bottom web is formed with a stretch ratio higher than 1.26, or

ii) the bottom web is heat-shrinkable and the sealed package is finally heat-shrunk.

A second object according to the invention is a flexible container thermoformed for dual-bake applications, comprising a thermoformed cavity and an opening, made by thermoforming a film of the above-mentioned bottom web, wherein the thermoformed cavity has a depth higher than 1 cm and/or the thermoformed container is heat-shrinkable.

A third object according to the invention is a dual ovenable, air tight thermoformed package comprising

A flexible, dual ovenable thermoformable container according to the second object, comprising a thermoformed cavity and an opening,

a food item to be placed in the cavity,

the opening is hermetically closed by a flexible container that is self-sealing at the opening or by a dual bakeable top web sealed to the container around the opening.

A fourth object of the invention is a method for cooking a food product comprising

-providing a dual ovenable thermoformed package enclosing said product, according to the third embodiment described above, and

-cooking the packaged food product in the package in a microwave oven or a conventional oven.

Brief Description of Drawings

Fig. 1 shows a cross-section of a deep-drawing container (201) according to the invention;

FIG. 2 shows pictures of thermoformed containers 2A, 2B made from commercial film (Mylar OL25 and Mylar OL40) and thermoformed container 2C made from film 7 suitable for use in the present invention;

FIG. 3 is a scheme of the "thermoforming-shrinking" process;

fig. 4 is a picture of a sausage thermoformed package according to the invention (fig. 4A, left) and a comparative package (fig. 4B, right) before shrinking;

fig. 5 is a photograph of the same sausage thermoformed package of fig. 4 but after shrinking (package according to the invention, fig. 5A, left; and comparative package, fig. 5B, right).

Definition of

As used herein, the term "film" refers to a plastic web, whether it be a film or sheet or a tube.

As used herein, the terms "inner layer" and "interior layer" refer to any film layer having its two major surfaces directly adhered to another layer of the film.

As used herein, the phrase "outer layer" or "exterior layer" refers to any film layer having only one major surface thereof directly adhered to another layer of the film. As used herein, the phrases "sealing layer", "sealing layer" and "sealant layer" refer to an outer layer that is related to a film to itself, sealed to another layer of the same or another film.

As used herein, the term "base layer" refers to a layer representing the largest part of the film in terms of thickness, in particular to a film layer having a thickness of at least 40%, preferably at least 50%, more preferably at least 60% of the total thickness of the film.

As used herein, the term "adhered" means that film layers having major surfaces are in direct or indirect contact with each other (through one or more additional layers therebetween) by coextrusion, extrusion coating, or by adhesive lamination.

As used herein, film layers that are "directly adhered" have major surfaces that are in direct contact with each other, with no adhesive or other layer between them.

As used herein, the term "polymer" refers to the product of a polymerization reaction and includes homopolymers and copolymers.

As used herein, the term "homopolymer" refers to a polymer polymerized from a single monomer, i.e., a polymer consisting essentially of a single type of mer (i.e., repeat unit).

As used herein, the term "copolymer" refers to a polymer formed from the polymerization of at least two different monomers.

As used herein, the term "polyolefin" refers to any polymeric olefin, which may be linear, branched, cyclic, aliphatic, aromatic, substituted or unsubstituted.A polyolefin includes olefin homopolymers, olefin copolymers, copolymers of olefins and non-olefinic comonomers copolymerizable with the olefin, such as vinyl monomers, modified polymers thereof, and the like.specific examples include ethylene homopolymers, propylene homopolymers, butene homopolymers, α -olefin copolymers of ethylene, and the like, propylene/α -olefin copolymers, butene/α -olefin copolymers, ethylene/unsaturated ester copolymers (e.g., ethylene/ethyl acrylate copolymers, ethylene/butyl acrylate copolymers, ethylene/methyl acrylate copolymers), ethylene/unsaturated acid copolymers (e.g., ethylene/acrylic acid copolymers, ethylene/methacrylic acid copolymers), ethylene/vinyl acetate copolymers, ionomer resins, polymethylpentene, and the like.

As used herein, the term "ethylene/α -olefin copolymer" refers to both heterophasic polymers and homogeneous polymers, such as those having a density typically of about 0.900 g/cm³To about 0.930 g/cm³Linear Low Density Polyethylene (LLDPE), in the range, typically having a density of about 0.930 g/cm³To about 0.945 g/cm³Linear Medium Density Polyethylene (LMDPE) in the range and density below about 0.915 g/cm³Usually 0.868 g/cm³To 0.915 g/cm³Very low and ultra low density polyethylene (VLDPE and ULDPE) in the range, as well as metallocene catalyzed Exact and Exceed homogeneous resins such as available from Exxon, Single site Affinity resins available from Dow and Tafmer homogeneous ethylene/α -olefin copolymer resins available from Mitsui all of these materials generally comprise a copolymer of ethylene with one or more comonomers selected from C4-10 α -olefins such as butene-1, hexene-1, octene-1, etc., wherein the molecules of the copolymer comprise long chains or crosslinked structures having relatively few side chain branches.

As used herein, the phrase "heterophasic polymer" or "polymer obtained by heterogeneous catalysis" refers to a polymerization reaction product of relatively wide variation in molecular weight and relatively wide variation in composition distribution, i.e., a typical polymer prepared, for example, using conventional Ziegler-Natta catalysts, e.g., a metal halide activated by an organometallic catalyst, i.e., titanium chloride optionally containing magnesium chloride complexed with a trialkylaluminum, and can be found in patents such as U.S. Pat. No. 4,302,565 to Goeke et al and U.S. Pat. No. 4,302,566 to Karol et al.

As used herein, the phrases "homogeneous polymer" or "polymer obtained by homogeneous catalysis" or "single site catalyzed (ssc) polymer" refer to a polymerization reaction product of relatively narrow molecular weight distribution and relatively narrow composition distribution homogeneous polymers differ structurally from heterogeneous polymers in that homogeneous polymers exhibit relatively uniform comonomer sequences within the chain, sequence distribution as a mirror image throughout the chain, and similar length throughout the chain, i.e., narrow molecular weight distribution.

Homogeneous ethylene/α -olefin copolymers (homogeneous EAOs) include modified or unmodified linear homogeneous ethylene/α -olefin copolymers sold as Tafmer @resinby Mitsui petrochemical corporation of Tokyo, Japan, modified or unmodified linear homogeneous ethylene/α -olefin copolymers sold as Exact @resinby Exxon Mobil Chemical Company of Houston, Tex., USA, and modified or unmodified homogeneous ethylene/α -olefin copolymers having long chain branching sold as Affinity brand resin by Dow Chemical Company.

As used herein, the term "modified" refers to chemical derivatives, for example, derivatives having any form of anhydride functionality, such as maleic anhydride, crotonic anhydride, citraconic anhydride, itaconic anhydride, fumaric anhydride, and the like, whether grafted onto, copolymerized with, or blended with one or more polymers, and also includes derivatives of such functionality, such as acids, esters, and metal salts derived therefrom.

As used herein, the phrase "modified polymer" and more specifically phrases such as "modified ethylene/vinyl acetate copolymer" and "modified polyolefin" refers to such polymers having anhydride functional groups as just defined grafted thereto and/or copolymerized therewith and/or blended therewith. Preferably, such modified polymers have anhydride functional groups grafted onto or polymerized with them, rather than merely blended with them.

As used herein, the phrases "anhydride-containing polymer" and "anhydride-modified polymer" refer to one or more of the following polymers: (1) polymers obtained by copolymerization of an anhydride-containing monomer with a second different monomer, and (2) anhydride-grafted copolymers, and (3) mixtures of polymers with anhydride-containing compounds.

As used herein, the term "modified polyolefin" includes modified polymers prepared by copolymerizing an olefin homopolymer or copolymer thereof with an unsaturated carboxylic acid such as maleic acid, fumaric acid, or the like or a derivative thereof such as an anhydride, ester, metal salt, or the like. It also includes a modified polymer obtained by blending or grafting an unsaturated carboxylic acid such as maleic acid, fumaric acid, etc. or a derivative thereof such as an acid anhydride, ester, metal salt, etc. with a polymer chain into an olefin homopolymer or copolymer.

Ethylene-unsaturated acid polymers include homopolymers and copolymers having acrylic and/or methacrylic acid linkages between monomer units. The acrylic acid-based resin may be formed by any method known to those skilled in the art and may include polymerization of acrylic acid or methacrylic acid in the presence of light, heat, or a catalyst such as benzoyl peroxide, or by esters of these acids followed by saponification. Examples of acrylic-based resins include, but are not limited to, ethylene/acrylic acid copolymers (EAA), ethylene/methacrylic acid copolymers (E/AA), and blends thereof.

Ethylene-unsaturated ester polymers include homopolymers and copolymers of esters having acrylic linkages between monomer units. The acrylate-based resin may be formed by any method known to those skilled in the art, such as by polymerizing an acrylate monomer in the same manner as described for the acrylic-based resin. Examples of acrylate-based resins include, but are not limited to, methyl/methacrylate copolymer (MMA), ethylene/vinyl acrylate copolymer (EVA), ethylene/methacrylate copolymer (EMA), ethylene/n-butyl acrylate copolymer (EnBA), and blends thereof.

As used herein, the phrase "ethylene/vinyl acetate" (EVA) refers to a copolymer formed from ethylene and vinyl acetate monomers in which the ethylene units are present in a large amount and the vinyl acetate units are present in a small amount. Typical amounts of vinyl acetate may range from about 5 wt% to about 20 wt%.

As used herein, the term "ionomer resin" refers to a copolymer based on a metal salt of a copolymer of ethylene and a vinyl monomer having an acid group, such as methacrylic acid, and is wherein the bonds are ionic (i.e., interchain ionic bonds) as well as covalent bonds. Ionomer resins have positively and negatively charged groups that do not associate with each other, thereby providing the resin with polar character. The metal may be in the form of a monovalent or divalent ion, such as lithium, sodium, potassium, calcium, magnesium, and zinc. Unsaturated organic acids include acrylic acid and methacrylic acid. Unsaturated organic esters include methacrylic acid esters and isobutyl acrylate. The ionomer resin may comprise a mixture of two or more ethylene/unsaturated organic acid or ester copolymers.

As used herein, the term "polyester" generally refers to a homopolymer or copolymer having ester linkages between monomer units, which may be formed, for example, by a polycondensation reaction between a dicarboxylic acid and a diol. The term "polyester" refers to both homopolyesters and copolyesters, wherein homopolyesters are defined as polymers obtained from the condensation of a dicarboxylic acid and a diol, and copolyesters are defined as polymers obtained from the condensation of one or more dicarboxylic acids and one or more diols.

The ester monomer units may be represented by the following general formula: r-c (O) O-R ', wherein R and R' are alkyl groups, and may generally be formed from the polymerization of dicarboxylic acid and diol monomers or monomers containing both carboxylic acid and hydroxyl moieties. The dicarboxylic acids may be linear or aliphatic, i.e., oxalic acid, malonic acid, succinic acid, glutaric acid, adipic acid, pimelic acid, suberic acid, azelaic acid, sebacic acid, and the like; or may be aromatic or alkyl-substituted aromatic acids, i.e., various isomers of phthalic acids, such as terephthalic acid (paraphthalic acid) (or terephthalic acid), isophthalic acid, and naphthalene dicarboxylic acid. Specific examples of the alkyl-substituted aromatic acid include various isomers of dimethyl phthalic acid such as dimethyl isophthalic acid, dimethyl phthalic acid, dimethyl terephthalic acid, various isomers of diethyl phthalic acid such as diethyl isophthalic acid, diethyl phthalic acid, various isomers of dimethyl naphthalene dicarboxylic acid such as 2, 6-dimethyl naphthalene dicarboxylic acid and 2, 5-dimethyl naphthalene dicarboxylic acid, and various isomers of diethyl naphthalene dicarboxylic acid. The diols may be linear or branched. Specific examples include ethylene glycol, propylene glycol, 1, 4-butanediol, neopentyl glycol, and the like. The polyalkylene terephthalate is an aromatic ester having a benzene ring having ester bonds at 1, 4-carbons of the benzene ring, as compared with the polyalkylisophthalate in which two ester bonds are present at 1, 3-carbons of the benzene ring. In contrast, poly (alkyl naphthalates) are aromatic esters having two fused benzene rings, where two ester linkages may be present at the 2, 3-carbon or 1, 6-carbon.

As used herein, unless otherwise specified, the term "polyester layer, film or container" refers to a layer, film or container comprising a major proportion of polyester, i.e., greater than 50 wt.%, preferably greater than 60 wt.%, 70 wt.%, 80 wt.%, 90 wt.% polyester relative to the layer or film, respectively.

Intrinsic Viscosity (IV), as used herein, is defined as the limit of reduced viscosity at infinite dilution of the polymer and is measured using a capillary viscometer. A suitable method for determining intrinsic viscosity is ASTM method D4603-03.

As used herein, the term "a substantial proportion" of resin in a layer, film or container means that greater than 50% by weight of the resin is present in the layer, film or container.

As used herein, the term "minor proportion" of resin in a layer, film or container means that less than 50% by weight of the resin is present in the layer, film or container.

As used herein, the term "thermoformed flexible container" refers to a thermoformed flexible pouch having an opening for loading a product to be packaged.

As used herein, the phrases "machine direction", abbreviated herein as "MD", and "machine direction", abbreviated herein as "LD", refer to the direction "along the length of the film", i.e., in the direction of extrusion of the film.

As used herein, the phrase "transverse direction," abbreviated herein as "TD," refers to a direction across the film that is perpendicular to the machine or machine direction.

As used herein, the term "extrusion" refers to a process of forming a continuous shape by forcing molten plastic material through a die, followed by cooling or chemical hardening. Immediately prior to extrusion through the die, the relatively high viscosity polymeric material is fed to a variable pitch rotating screw, i.e., an extruder, which forces the polymeric material through the die.

As used herein, the term "coextrusion" refers to the process of extruding two or more materials through a single die having two or more orifices arranged such that the extrudates merge and fuse together to form a sheet-like structure, which is then frozen, i.e., quenched.

As used herein, the term "oriented" means that a thermoplastic web is drawn in one direction ("uniaxial") or two directions ("biaxial") at a temperature above the softening temperature, and then the film is cooled to "set" it while substantially maintaining the drawn dimensions. Solid state orientation at temperatures above the softening point produces films that exhibit heat shrink characteristics upon subsequent heating. Orientation in the molten state, as in the manufacture of blown films, does not result in heat-shrinkable films. Orientation in both the molten and solid states increases the degree of alignment of the polymer chains, thereby enhancing the mechanical properties of the resulting oriented film.

As used herein, the term "vacuum forming" is a thermoforming process in which air is evacuated from the sealed space between a hot sheet and a mold, allowing atmospheric pressure to force the sheet to conform to the contours of the mold.

As used herein, the term "standard thermoforming or shallow thermoforming" refers to thermoforming characterized by a low stretch ratio, i.e., less than 1.26, which provides a shallow cavity.

As used herein, "deep drawing or deep drawing thermoforming" generally refers to thermoforming of thermoplastic materials characterized by a draw ratio greater than 1.26, preferably greater than 2.0, 2.5, 3.0, 3.5, 4.0, or 4.5, which provides a deep cavity.

As used herein, the term "thermoformable" is defined as a material that is "thermoformable" upon heating on a suitable apparatus, i.e., a material that can be shaped upon exposure to pressure and/or vacuum. The material has a thermoplastic such that it can be deformed when heated, but exhibits sufficient dimensional stability at room temperature to retain the shape predetermined by thermoforming.

As used herein, the term "deep drawable" is defined as a material that can be stretched at a stretch ratio of greater than 1.26, preferably greater than 2.0, more preferably greater than 2.5, 3.0, 3.5, 4.0, or 4.5.

As used herein, the term "thermoforming draw ratio" (DR) refers to the draw ratio calculated on the mold, in particular the ratio between the total surface area of the mold and the footprint of the mold.

As used herein, the term "actual thermoforming stretch ratio" (a-DR) refers to the actual ratio at which the film is stretched under thermoforming. The actual draw ratio may be calculated from the actual dimensions of the thermoformed container.

As used herein, the term "cavity" refers to a recessed portion obtainable by thermoforming a thermoplastic material surrounded by a raised outer or peripheral portion.

As used herein, the terms "heat-shrinkable", and the like refer to a film that shrinks when heated, i.e., the tendency to shrink when heated, such that the size of the film decreases when the film is in an unconstrained state. Free shrinkage is the percent dimensional change of a 12 cm x 12 cm film sample when heated in an oven at 180 ℃ for 5 minutes, as explained in the test methods section.

As used herein, unless otherwise specified, the term "heat shrinkage" or "percent free shrink" refers to the shrink properties of the film prior to thermoforming.

As used herein, the term "non-heat shrinkable" means that the film is characterized by a total free shrink percentage (i.e., the sum of the percent free shrink in the LD and TD directions) of less than 5%, said percentage being measured in an oven at 180 ℃ according to the test method reported in the experimental section.

As used herein, the term "microwaveable" refers to "substantially microwave transparent" structures as well as "microwave active" structures. While substantially microwave transparent are those structures that are capable of being passed through by at least 80%, preferably at least 90%, of the microwaves generated by a microwave oven without any interference therefrom, microwave activity is those structures that incorporate microwave reflective components intended to alter energy deposition within adjacent food products. For "microwaveable" in both cases, the packaging material should not degrade or deform under conditions of use, and it should not release more than 60 ppm of the overall contaminant to the packaged food product with which it is in contact. Indeed, according to most food methodologies, packaging materials that are subjected to a heat treatment at 121 ℃ for 30 minutes (a sufficiently drastic condition that is not normally reached in microwave cooking) without deforming and releasing less than 60 ppm of contaminants are considered "microwaveable".

As used herein, the term "dual ovenable" refers to a film or package suitable for both microwave oven cooking and conventional oven cooking that is capable of withstanding cooking temperatures above 205 ℃ and up to 220 ℃.

All percentages in this specification are weight percentages unless otherwise indicated.

Detailed Description

A first object of the invention is a thermoformed food packaging process for making a dual ovenable thermoformed package comprising

Providing a thermoformable, dual bakeable biaxially oriented polyester film as a base web,

-forming the bottom web so as to provide at least cavities having openings;

-placing a food product in the cavity through the opening;

-cutting out the sealed packages,

characterized in that the bottom web comprises:

an outer heat sealable polyester layer a),

an inner polyester base layer b) comprising a polyester having an Intrinsic Viscosity (IV) higher than 0.75 dl/g measured according to ASTM D4603-03,

an outer polyester layer c), and

i) the bottom web is formed with a stretch ratio higher than 1.26, or

ii) the bottom web is heat-shrinkable and the sealed package is finally heat-shrunk.

The outer heat sealable polyester layer a) of the film comprises at least 80 wt.%, preferably at least 85 wt.%, relative to the weight of the layer, of one or more polyesters.

The composition of the heat-sealable polyester layer a) may vary to some extent provided that it is sealed to the polyester material at a temperature below the melting temperature of the resins of the base layer b) and the outer layer c).

The seal must be strong enough to prevent the package from leaking during storage and transport, but at the same time it must allow self-venting during cooking and easy opening of the package by the end consumer after cooking.

Suitable heat-sealable polyester compositions for layer a) are known and described, for example, in WO2007093495 or WO 2012160142.

In one embodiment, the polyester of the heat-sealable layer a) may be an amorphous polyester or a crystalline polyester, the melting temperature of which is not higher than the melting temperature of the polyester of the base layer b), or a mixture thereof, according to WO 2007093495.

The term "crystalline" is used herein to indicate that the resin has a defined melting temperature.

The heat-sealable layer a) may comprise an amorphous copolyester resin or a crystalline copolyester resin having a melting temperature lower than that of the polyester of the base layer b).

As polyester resin of the heat-sealable layer a) it is possible to use copolyester resins derived from one or more dicarboxylic acids or their lower alkyl (up to 14 carbon atoms) diesters with one or more glycols, in particular aliphatic or cycloaliphatic glycols.

Suitable dicarboxylic acids include aromatic dicarboxylic acids such as terephthalic acid, isophthalic acid, phthalic acid or 2,5-, 2, 6-or 2, 7-naphthalenedicarboxylic acid, and aliphatic dicarboxylic acids such as succinic acid, sebacic acid, adipic acid, azelaic acid, suberic acid or pimelic acid. Suitable diols include aliphatic diols such as ethylene glycol, diethylene glycol, triethylene glycol, propylene glycol, 1, 3-butanediol, 1, 4-butanediol, 1, 5-pentanediol, 2-dimethyl-1, 3-propanediol, neopentyl glycol, and 1, 6-hexanediol, and cycloaliphatic diols such as 1, 4-cyclohexanedimethanol and 1, 4-cyclohexanediol.

In one embodiment, the heat-sealable layer a) comprises a crystalline copolyester according to WO 2007093495.

Crystalline copolyesters are copolyesters having at least one distinct melting peak in a Differential Scanning Calorimetry (DSC) thermogram. The melting point of the resin can be measured by using DSC technique according to ASTM D3418.

Preferably, the crystalline copolyester of the heat-sealable layer comprises an aromatic dicarboxylic acid and an aliphatic dicarboxylic acid. The preferred aromatic dicarboxylic acid is terephthalic acid. Preferred aliphatic dicarboxylic acids are selected from sebacic acid, adipic acid and azelaic acid. The concentration of the aromatic dicarboxylic acid present in the copolyester is preferably in the range of 45 to 80 mol%, more preferably in the range of 50 to 70 mol%, and particularly in the range of 55 to 65 mol%, based on the dicarboxylic acid component of the copolyester. The concentration of the aliphatic dicarboxylic acid present in the copolyester is preferably in the range of 20 to 55 mol%, more preferably in the range of 30 to 50 mol%, and particularly in the range of 35 to 45 mol%, based on the dicarboxylic acid component of the copolyester. Particularly preferred examples of suitable copolyesters are (i) copolyesters of azelaic acid and terephthalic acid with an aliphatic diol, preferably ethylene glycol; (ii) copolyesters of adipic acid and terephthalic acid with an aliphatic diol, preferably ethylene glycol; and (iii) copolyesters of sebacic acid and terephthalic acid with an aliphatic diol, preferably butanediol. Preferred copolyesters include the sebacic acid/terephthalic acid/butanediol copolyester having a melting point Tm of 117 c, and azelaic acid/terephthalic acid/ethylene glycol copolyester having a melting point Tm of 150 c.

In one embodiment, the copolyester of the heat-sealable layer a) is derived from an aliphatic diol and a plurality of aromatic dicarboxylic acids, in particular terephthalic acid and isophthalic acid, according to WO 2007093495. Preferred copolyesters are derived from ethylene glycol, terephthalic acid, and isophthalic acid. The preferred molar ratio of terephthalic acid component to isophthalic acid component is in the range of 50:50 to 90:10, preferably in the range of 65:35 to 85: 15.

In one embodiment, the heat-sealable layer a) comprises an amorphous copolyester according to WO 2007093495.

Suitable amorphous copolyesters are those derived from aliphatic and cycloaliphatic diols with one or more dicarboxylic acids, preferably aromatic dicarboxylic acids. Typical polyesters which provide satisfactory heat sealability include copolyesters of terephthalic acid with aliphatic and cycloaliphatic diols, particularly ethylene glycol and 1, 4-cyclohexanedimethanol. The preferred molar ratio of cycloaliphatic diol to aliphatic diol is in the range of 10:90 to 60:40, preferably in the range of 20:80 to 40:60, and more preferably in the range of 30:70 to 35: 65. An example of such a copolyester is PETG Eastar 96763 sold by Eastman, which comprises a copolyester of terephthalic acid, about 33 mole% 1, 4-cyclohexanedimethanol, and about 67 mole% ethylene glycol, and has a glass transition temperature Tg of 81 ℃.

In order to reduce the seal strength and thus facilitate opening of the package, it may be convenient to blend the one or more polyester resins of the heat-sealable outer layer a) with from 3 to 40% by weight, from 5 to 30% by weight, preferably from 15 to 25% by weight of a suitable thermoplastic resin. Suitable thermoplastic resins which help to reduce the seal strength without impairing the optical properties of the film are polyamides, polystyrenes, in particular styrene-butadiene block copolymers, ionomers, ethylene/unsaturated carboxylic acid copolymers, such as ethylene/(meth) acrylic acid copolymers, ethylene/unsaturated ester copolymers, such as ethylene/vinyl acetate copolymers, maleic anhydride-modified polyethylene, ethylene/propylene copolymers and ethylene/cycloolefin copolymers, such as ethylene/norbornene copolymers.

By blending the amorphous copolyester with 3 to 40 wt% of ethylene/acrylic acid copolymer or ethylene/propylene copolymer or maleic anhydride modified polyethylene, a good balance between hermetic sealing and easy removal of the film upon opening of the package can be obtained. Good results were obtained by blending PET with 3 to 40 wt.% polyamide. Suitable polyamides are, for example, polyamide 6, polyamide 66 and copolyamides, including copolyamide 6/9, copolyamide 6/10, copolyamide 6/12, copolyamide 6/66, copolyamide 6/69, and aromatic polyamides and copolyamides such as 61, 6I/6T, MXD6, MXD 6/MXDI.

Blends of amorphous copolyesters with 3 to 40 weight percent ethylene/acrylic acid copolymer are particularly useful in packaging applications requiring heat treatment, such as pasteurization, because they provide the best balance between package openability and air-tightness. An example of a suitable amorphous polyester is PETG Eastar 6763 sold by Eastman.

According to WO2012160142, when heating or cooking at higher temperatures in a conventional oven is required, the heat-sealable layer a) comprises, in addition to about 25 to 70% by weight of at least a first amorphous polyester (whose melting temperature is not higher than that of the polyester of the base layer b) and 10 to 20% by weight of at least a thermoplastic resin, 20 to 60% by weight of at least one further polyester resin (ternary blend).

Suitable amorphous polyester resins are those derived from aliphatic and cycloaliphatic diols with one or more dicarboxylic acids, preferably aromatic dicarboxylic acids. Preferably, said amorphous polyester is chosen from those derived from aliphatic and cycloaliphatic diols and one dicarboxylic aromatic acid, more preferably terephthalic acid. Preferred amorphous polyesters are copolyesters of terephthalic acid with aliphatic and cycloaliphatic diols, especially ethylene glycol and 1, 4-dicyclohexyldimethanol.

The preferred molar ratio of cycloaliphatic diol to aliphatic diol is in the range of from 10:90 to 60:40, preferably in the range of from 20:80 to 40:60, more preferably in the range of from 30:70 to 35: 65. A specific example of a particularly preferred amorphous polyester is PETGEstar 6763 sold by Eastman, which comprises a copolyester of terephthalic acid, about 33 mole% 1, 4-cyclohexanedimethanol, and about 67 mole% ethylene glycol.

In a particularly preferred embodiment, the amorphous polyester resin in the heat-sealable layer is the same as the polyester resin used in the base layer.

Suitable thermoplastic resins are polyamides, polystyrenes, in particular styrene-butadiene block copolymers, polyethylenes, ionomers, ethylene/unsaturated carboxylic acid copolymers, such as ethylene/(meth) acrylic acid copolymers, ethylene/unsaturated ester copolymers, such as ethylene/vinyl acetate copolymers, ethylene/propylene copolymers, maleic anhydride-modified polyethylenes, such as modified LLDPE and ethylene/cycloolefin copolymers, such as ethylene/norbornene copolymers. Ethylene/(meth) acrylic acid copolymers and modified LLDPE are preferred. Specific examples of particularly preferred thermoplastic resins are Primacor 3440 sold by Dow, which is an ethylene/acrylic acid copolymer having a comonomer acrylic acid content of 9.7%, BYNEL 4104 (2006) sold by DuPont, which is a maleic anhydride modified ethylene/butene copolymer and a modified LLDPE.

Suitable further polyesters are those derived from one or more aliphatic diols, preferably ethylene glycol and/or cyclohexanedimethanol, and aromatic dicarboxylic acids, preferably terephthalic acid. Suitable further polyesters are preferably characterized by an intrinsic viscosity of at least 0.75 dl/g or more and/or an intrinsic viscosity having a glass transition temperature Tg of not higher than 80 ℃ and/or a melting point higher than 240 ℃. A suitable method for determining intrinsic viscosity is ASTM method D4603-03. A suitable method for determining the glass transition temperature is, for example, ASTM method D-3418. A suitable method for determining the melting point is for example ASTM method D3418.

Polyethylene terephthalate (PET) is preferred. Specific examples of other polyesters are PET sold by Eastman Chemical under the name Eastapak copolyester 9921, or RAMAPET N180 sold by Inderama Polyester.

The amount of the first amorphous polyester in the heat-sealable layer of the multilayer film according to the present invention is typically from 25 to 70% by weight, preferably from 40 to 60% by weight, relative to the total weight of the heat-sealable layer. Particularly preferred amounts are about 40 wt% and about 60 wt%.

The amount of thermoplastic resin in the heat-sealable layer of the multilayer film according to the present invention is generally from 10 to 20% by weight, preferably about 15% by weight, relative to the total weight of the heat-sealable layer.

The amount of the further polyester in the heat-sealable layer of the multilayer film according to the present invention is typically from 20 to 60 wt%, preferably from 25 to 50 wt%, relative to the total weight of the heat-sealable layer. Particularly preferred amounts are about 25 wt%, about 45 wt% and about 60 wt%.

In a preferred embodiment, the heat-sealable layer a) comprises about 25 to 70% by weight of amorphous polyester, 10 to 20% by weight of thermoplastic resin and 20 to 60% by weight of other polyester.

In a particularly preferred embodiment, the heat-sealable layer a) comprises about 40 to 60% by weight of the first amorphous polyester, 25 to 50% by weight of the further polyester and 10 to 20% by weight of the thermoplastic resin.

Specific examples of blends of at least amorphous polyester, at least thermoplastic resin and at least other polyester in the heat-sealable layer a) are:

i) 60% of a first amorphous polyester; 15% of thermoplastic resin; 25% of other polyesters;

ii) 40% of a first amorphous polyester; 15% of thermoplastic resin; 45% of other polyesters; and

iii) 25% of a first amorphous polyester; 15% of thermoplastic resin; the other polyester was 60%.

A particularly preferred ternary blend of layer a) consists of 60% PETG, 15% modified LLDPE and 25% PET.

Another particularly preferred ternary blend of layer a) consists of 60% by weight of PETG, 15% of ethylene/acrylic acid copolymer and 25% of PET.

Preferably, the thickness of the sealing layer (a) is 0.5 to 25 microns, preferably 1 to 20 microns, more preferably 1 to 15 microns, even more preferably 2 to 10 microns.

The percentage of the thickness of the heat-sealable polyester layer a) to the total thickness of the film is generally from 2 to 30%, preferably from 3 to 25% or from 6 to 20%.

The percentage of the thickness of the heat-sealable polyester layer a) to the total thickness of the film is typically less than 30%, less than 25%, less than 20%, less than 15% or less than 10%.

The inner polyester base layer b) of the film used in the present invention comprises at least a polyester having an intrinsic viscosity higher than 0.75 dl/g measured according to ASTM D4603-03.

Preferably, the base layer of the film comprises a polyester having an intrinsic viscosity higher than 0.78, more preferably at least 0.80 dl/g.

The polyester resin used as starting material for the base layer b) may also have an intrinsic viscosity lower than 0.75 dl/g, provided that its intrinsic viscosity after extrusion is higher than said value. For example, the intrinsic viscosity of the polyester resin may be increased during the extrusion process by suitable additives such as so-called "chain extenders". Suitable chain extenders are, for example, those described in EP 372846.

Suitable polyester resins are, for example, polyesters of ethylene glycol and terephthalic acid, i.e. poly (ethylene terephthalate) (PET). Preferred are polyesters comprising ethylene units and comprising at least 90 mole%, more preferably at least 95 mole%, terephthalate units based on dicarboxylate units. The remaining monomer units are selected from other dicarboxylic acids or diols. Suitable further aromatic dicarboxylic acids are preferably isophthalic acid, phthalic acid, 2,5-, 2, 6-or 2, 7-naphthalenedicarboxylic acid. Among the cycloaliphatic dicarboxylic acids, cyclohexane dicarboxylic acids (especially cyclohexane-1, 4-dicarboxylic acid) should be mentioned. Among the aliphatic dicarboxylic acids, the (C3-C19) alkanedioic acids are particularly suitable, in particular succinic acid, sebacic acid, adipic acid, azelaic acid, suberic acid or pimelic acid.

Suitable further aliphatic diols are, for example, aliphatic diols, such as ethylene glycol, diethylene glycol, triethylene glycol, propylene glycol, 1, 3-butanediol, 1, 4-butanediol, 1, 5-pentanediol, 2-dimethyl-1, 3-propanediol, neopentyl glycol and 1, 6-hexanediol, and cycloaliphatic diols, such as 1, 4-cyclohexanedimethanol and 1, 4-cyclohexanediol, optionally with one or more rings, heteroatom-containing diols.

Mixtures or blends of homopolyesters and/or copolyesters may be used for the base layer b), provided that the polyester with an IV above 0.75 dl/g makes up a large proportion of the base layer. The base layer b) comprises more than 50 wt. -%, preferably more than 60 wt. -%, 70 wt. -%, 80 wt. -%, 85 wt. -%, 90 wt. -% or 95 wt. -% of a polyester having an IV of more than 0.75 dl/g, based on the total weight of the base layer. Any homopolyester and/or copolyester may be blended with a polyester resin having an IV above 0.75 dl/g in the base layer b).

Preferably, the base layer comprises greater than 50, 60, 70, 80, 85, 90 or 95 wt% PET having an IV of at least 0.80 dl/g.

Examples of polyesters suitable for layer b) are PET 9921W ® commercially available from Voridian, RAMETN 180 from Indomam having a melting point Tm of 245 ℃ and an IV of 0.80 dl/g, or EASTAPAK 9921 from Eastman Chemical having a Tm of 238 ℃ and an IV of 0.8 dl/g.

Suitable blends for the substrate layer b) may comprise at least 50%, 60%, 70%, 80%, 85%, 90%, 95% polyester resin having an IV above 0.75 dl/g and no more than 50%, 40%, 30%, 20%, 15%, 10%, 5% amorphous polyester resin. The amorphous polyester used in the base layer may be the same as or different from the amorphous polyester used in the heat sealable layer.

Suitable amorphous polyester resins for the substrate are copolyesters of terephthalic acid with aliphatic and cycloaliphatic diols, especially ethylene glycol and 1, 4-cyclohexanedimethanol, such as PETG Eastar 6763 sold by Eastman Chemical.

Suitable substrate layers b) comprise at least 50%, 60%, 70%, 80%, 85%, 90%, 95% of a polyester resin having an IV above 0.75 dl/g and not more than 50%, 40%, 30%, 20%, 15%, 10%, 5% of an amorphous polyester of terephthalic acid with ethylene glycol and 1, 4-cyclohexanedimethanol.

In one embodiment, layer b) consists of polyester.

The choice of polyester with an intrinsic viscosity higher than 0.75 dl/g for the base layer b) of the film of the invention provides unexpectedly good formability, high draw ratio, very good conformability to the mould, minimal shrinking effect on removal from the mould and high shrinkage after thermoforming, as shown in inventive examples 1, 2 and 4, compared to commercial films based on conventional polyester.

The thermoformability of the film can be further improved by preferably incorporating a plasticizer in the base layer. Suitable plasticizers include aromatic dicarboxylic acid esters such as dimethyl phthalate, diethyl phthalate, di-n-butyl phthalate, di-n-hexyl phthalate, di-n-heptyl phthalate, di-2-ethylhexyl phthalate, di-n-octyl phthalate, di-n-nonyl phthalate, diethyl isophthalate, di-n-butyl isophthalate, di-2-ethylhexyl isophthalate, diethyl terephthalate, di-n-butyl terephthalate, di-2-ethylhexyl terephthalate, and the like; phosphoric esters such as triethyl phosphate, tri-n-butyl phosphate, trioctyl phosphate, tolyl phosphate, and the like; sebacates such as dimethyl sebacate, diethyl sebacate, di-n-butyl sebacate, dipentyl sebacate, and the like; adipates such as adipic acid adipate, and the like; esters such as butyl phthalyl butyl glycolate, tributyl citrate, tetrahydrofurfuryl oleate, methylacetyl ricinoleate, etc.; and polyethylene glycol and the like.

In one embodiment, the plasticizer is selected from aromatic dicarboxylic acid esters (particularly phthalates) because they have excellent heat resistance, can significantly improve thermoformability, and do not have the problems of sublimation and exudation during the film forming process.

The melting point of the plasticizer is preferably at least 300 ℃ or higher, more preferably at least 350 ℃. The plasticizer content in the layer is preferably from 0.01 to 5%, more preferably from 0.05 to 2%, based on the weight of the polymeric material of the layer.

The percentage of the thickness of the polyester base layer b) to the total thickness of the film is typically 40% to 90%, preferably 50% to 85%, or 60% to 80%.

The percentage of the thickness of the polyester base layer b) to the total thickness of the film is preferably higher than 50%, preferably higher than 60%, 65% or 70%.

The film for the use according to the invention is preferably a three-layer structure comprising, in addition to the base layer b) and the first outer heat-sealable layer a), a second outer polyester layer c) preferably adhered directly to the opposite side of the base layer b).

The outer polyester layer c) of the film preferably comprises at least 80 wt.%, preferably at least 85 wt.%, at least 90 wt.% of one or more polyesters relative to the weight of the layer.

In one embodiment, layer c) is comprised of polyester.

The one or more polyester resins of the layer c) may be the same as or different from, preferably the same as, the resin of the base layer b).

Preferably, the second outer polyester layer c) comprises a polyester characterized by an intrinsic viscosity of at least 0.75 dl/g or higher measured according to ASTM D4603-03 and/or a glass transition temperature Tg not higher than 80 ℃ measured according to ASTM D3418 and/or a melting point higher than 240 ℃.

Examples of suitable polyesters for the outer layer c) are EASTAPAK 9921 from Eastman Chemical or RAMAPE N180 from Indomaapolyester.

The thickness of the outer layer c) is generally from about 5% to 40%, preferably from 10% to 35%, more preferably from 15% to 30% of the total thickness of the film.

The thickness of the outer layer c) may be up to about 25 microns, preferably up to about 15 microns or 10 microns, more preferably from about 0.5 to 10 microns, and more preferably from about 0.5 to 7 microns.

The thicknesses of the two outer layers may be the same or different.

One or more layers of the film of the present invention may contain any of the additives conventionally used in the manufacture of polymeric films. Therefore, agents such as pigments, lubricants, antioxidants, radical scavengers, UV absorbers, heat stabilizers, antiblocking agents, surfactants, slip agents, fluorescent whitening agents, gloss improvers, viscosity modifiers may be appropriately incorporated.

In particular, slip and/or antiblock agents may be added to one or both outer layers in order to improve processing of the film in high speed packaging equipment. The additives may be added as a concentrate in the polyester carrier resin. The amount of additive is typically on the order of 0.2 to 5 wt% of the total weight of the layer.

In case the package is not under vacuum, the film of the invention preferably comprises at least one surface with anti-fogging properties. Typically, the anti-fog surface is the surface of the heat-sealable layer that directly faces the product.

To obtain an antifog surface, the antifog agent may be compounded directly into the polyester resin of the heat-sealable layer prior to extrusion of the film for use in the present invention. Suitable antifogging agents are, for example, nonionic fluorinated surfactants such as fluorinated alkyl esters, perfluoroalkyl oxiranes, anionic fluorinated surfactants such as quaternary ammonium salts of perfluoroalkyl sulfonate esters, nonionic surfactants such as polyol fatty acid esters, higher fatty acid amines, higher fatty acid amides and ethylene oxide adducts of higher fatty acid amines or amides, and the like. The amount of antifog agent added to the heat-sealable layer is typically from 0.5 to 8%, from 1 to 5%, from 1 to 3% by weight of the heat-sealable layer.

Alternatively, the antifog agent may be in the form of a coating applied to the heat sealable outer layer. The antifog agent may be applied to the heat sealable layer using conventional techniques, such as gravure coating, reverse kiss coating, dampening bar coating, or spray coating.

The application of the antifogging agent may be performed during the manufacture of the polyester film by an in-line process comprising application, or after the manufacture of the polyester film by an off-line coating process comprising application.

Suitable antifogging agents for such applications are nonionic surfactants such as polyol fatty acid esters, higher fatty acid amines, higher fatty acid amides, polyoxyethylene ethers of higher fatty alcohols, and ethylene oxide adducts of higher fatty acid amines or amides. Among them, polyhydric alcohol fatty acid esters, polymethylene ethers of higher fatty alcohols, and glycerin fatty acid esters are preferable.

The amount of the antifogging agent coating is not particularly limited, butIt may be from 0.1 to 8 ml/m²0.5 to 7 ml/m²0.5 to 5 ml/m²。

The thickness of the outer layer c) may be up to about 25 microns, preferably up to about 15 microns, more preferably from 0.5 to 10 microns, and more preferably from about 0.5 to 7 microns. The thicknesses of the two outer layers may be the same or different.

The film for use in the present invention may have any total thickness of 10 to 100 microns, 15 to 75 microns, more preferably 15 to 50 microns or 15 to 35 microns.

Preferably, the film of the invention has a thickness of less than 50 microns, more preferably less than 40 microns, even more preferably less than 35 microns, 30 microns or 25 microns prior to thermoforming.

Preferably, the film has a thickness of greater than 10 microns, preferably greater than 12 microns, more preferably greater than 15 microns prior to thermoforming.

Preferably, the film has a thickness of 10 to 100 microns, preferably 15 to 75 microns, more preferably 15 to 50 microns or 15 to 35 microns prior to thermoforming.

Preferably, when the film is thermoformed in deep drawing, its total thickness before thermoforming is at least 15 microns, preferably 20 microns, more preferably 25 microns or 30 microns.

Preferably, the thickness of the film measured at the bottom of the thermoformed cavity after thermoforming is below 20 microns, preferably below 15 microns.

The polyester films used in the present invention are advantageous over the currently marketed dual-bakeable thermoformable films, which provide comparable performance at lower thicknesses.

The polyester film used in the present invention may comprise a base layer b), a first outer heat-sealable layer a) and a second outer layer c), wherein the second outer layer c) comprises a polyester resin different from the resins used in the base layer and the heat-sealable layer.

Alternatively, the polyester film may comprise a base layer b) and two outer heat-sealable layers a) comprising the same amorphous polyester or the same crystalline polyester, the melting temperature of which is not higher than the melting temperature of the polyester of the base layer.

Alternatively, the polyester film may comprise a base layer b), a first outer heat-sealable layer a) and a second outer layer c), wherein the second outer layer c) comprises the same polyester resin as the base layer b).

In one embodiment, the polyester film used in the present invention comprises a base layer b) comprising a polyester having an intrinsic viscosity of above 0.75 dl/g, a first outer heat sealable layer a) comprising an amorphous polyester and a second outer layer c) comprising the same polyester resin as the base layer.

In one embodiment, the polyester film used in the present invention comprises a base layer b) comprising a polyester having an intrinsic viscosity higher than 0.75 dl/g, a first outer heat sealable layer a) comprising a ternary blend of an amorphous polyester, a thermoplastic resin and a further polyester, and a second outer layer c) comprising the same polyester resin as the base layer.

Preferably, the polyester film comprises a base layer b) comprising at least 50%, 60%, 70%, 80%, 85%, 90%, 95% of a polyester resin having an IV above 0.75 dl/g and no more than 50%, 40%, 30%, 20%, 15%, 10%, 5% of an amorphous polyester; a first outer heat sealable layer a) comprising an amorphous polyester; and a second outer layer c) comprising the same polyester resin as the base layer. Preferably, the amorphous polyester in the base layer b) is the same as the amorphous polyester in the heat-sealable layer a).

In one embodiment, the polyester film for use in the present invention comprises:

a heat-sealable layer a) comprising

About 25 to 70 weight percent of at least a first amorphous polyester having a melting temperature not higher than the melting temperature of the polyester of the base layer b),

20 to 60 wt% of at least another polyester characterized by an intrinsic viscosity of at least 0.75 dl/g or higher measured according to ASTM D4603-03 and/or a glass transition temperature Tg of not higher than 80 ℃ measured according to ASTM D3418 and/or a melting point of higher than 240 ℃; and/or

-an inner polyester substrate b) comprising a mixture of at least 50% of a polyester resin having an IV higher than 0.75 dl/g and at most 50% of an amorphous polyester; and/or

-an outer polyester layer c) comprising a polyester characterized by an intrinsic viscosity of at least 0.75 dl/g or higher measured according to ASTM D4603-03 and/or a glass transition temperature Tg not higher than 80 ℃ measured according to ASTM D3418 and/or a melting point higher than 240 ℃.

Preferably, the polyester film for use in the present invention consists of:

a heat-sealable layer a) comprising

About 25 to 70 weight percent of at least a first amorphous polyester having a melting temperature not higher than the melting temperature of the polyester of the base layer b),

-an inner polyester substrate b) comprising a mixture of at least 50% of a polyester resin having an IV higher than 0.75 dl/g and at most 50% of an amorphous polyester; and

In one embodiment, the polyester film for use in the present invention consists of:

-a heat-sealable layer a) consisting of:

about 40 to 70 weight percent of at least a first amorphous polyester having a melting temperature not higher than the melting temperature of the polyester of the base layer b),

20 to 50 wt% of at least another polyester characterized by an intrinsic viscosity of at least 0.75 dl/g or higher and/or a glass transition temperature Tg not higher than 80 ℃ and/or a melting point higher than 240 ℃; and

-an inner polyester substrate b) consisting of a mixture of at least 55% of a polyester resin having an IV higher than 0.75 dl/g and at most 45% of an amorphous polyester; and

-an outer polyester layer c) comprising at least 95% of the same polyester as the base layer b), said polyester being characterized by an intrinsic viscosity of at least 0.75 dl/g.

Preferred membranes for use in the present invention are membranes consisting of:

-an outer heat-sealable layer a) consisting of about 60% by weight of PETG, 25% by weight of PET and 15% by weight of modified LLDPE or EAA;

-an inner base layer b) consisting of about 60% by weight of PET with an IV higher than 0.75 dl/g and 40% by weight of PETG; and

-an outer polyester layer c) consisting of about 98% by weight of the same PET as the base layer and 2% by weight of PETG.

Exemplary films useful in the present invention and methods of making the same are described in WO2012160142 and WO 2007093495.

Other possible films and their preparation are disclosed in WO2009013284 (e.g., the film of example 2) and WO2013080143 in the name of Cryovac.

The applicant has surprisingly found that the above polyester films exhibit such good formability and shrinkage that they can be advantageously used in deep drawing and/or thermoforming-shrinking applications. In a preferred embodiment, the film is used in a deep draw thermoforming-shrink wrapping process.

The formability of the polyester film used in the method of the present invention can be evaluated visually after the thermoforming cycle, by calculating the thermoforming draw ratio or preferably by measuring the actual volume of the thermoformed cavity.

The thermoforming draw ratio represents a theoretical value of formability, calculated based on the mold size as follows:

draw ratio = surface area of mold/footprint of mold.

An example of calculating the draw ratio for a 2 cm deep parallelepiped mold is as follows:

the size of the die is as follows: 10 cm long x 12 cm wide x 2 cm deep

Surface area: 2(10 cm x 2 cm) + 2(12 cm x 2 cm) + (10 cm x 12 cm) = 208 cm²

The occupied area is as follows: 10 cm x 12 cm = 120 cm²

Stretching ratio: = 1.7

The draw ratio represents the maximum draw that a material can experience in a mold if the material ideally conforms to the mold.

Preferably, in the deep drawing process according to the invention, the draw ratio in the forming step is higher than 2.0, more preferably higher than 2.5, 3.0, 3.5, 4.0 or 4.5.

However, depending on the formability of the film and the mold configuration, the actual stretch ratio (i.e., the stretch ratio evaluated on the thermoformed container) may even differ significantly from the theoretical value.

The actual stretch ratio can be difficult to calculate, particularly in the case of irregularly shaped or ribbed containers.

The evaluation of the formability of the film can be more easily performed by comparing the actual volume of the thermoforming cavity of the container with the volume of the mold. These volumes can be evaluated indirectly based on the weight of water required to fill the cavity or mold, respectively, as explained under the "volume test" (shrinkage index after thermoforming) in this experimental section.

The difference in volume (or water weight) of the cavity and the mold is related to the formability of the tested material.

This volume difference can be calculated as explained later according to the following formula:

Δ V% = [ (V cavity-V mold)/V mold ] x 100= [ (Ww cavity-Ww mold)/Ww mold ] x 100

Where V is the volume of the cavity or mold (e.g., in cc) and Ww is the weight of water filled in the cavity or mold, in grams. The more negative the percentage, the more the film retracts after being removed from the mold.

The polyester film used in the thermoforming process of the invention is characterized by a difference in volume percentage typically below-35%, preferably below-30% or below-25%, which means that the actual volume of the thermoformed cavity is very close to the original volume of the mold. For the commercial comparative film Mylar tested in this experimental section, this difference was typically quite significant, i.e., above-35%, such as-40% or higher, meaning that even with the same draw specific heat, the commercial film was less formable and produced a cavity of significantly smaller volume (see the pictures of fig. 2A-2C).

The film used as the base web according to the invention may be heat-shrinkable or non-heat-shrinkable.

In one embodiment of the deep draw packaging process, the polyester film may be non-heat shrinkable, i.e. having a percentage free shrinkage in both the LD and TD directions of less than 3%, preferably less than 2%.

In this case, after orientation, the polyester film is heat-set by a tailored annealing step.

Preferably, the polyester film used in the deep-drawing food packaging method may be heat-shrinkable. Advantageously, the film of the invention is endowed with very good shrink properties even after thermoforming, providing a very compact and attractive package to be finally heated.

In thermoforming-shrink applications, the polyester film is heat shrinkable both before and after thermoforming.

In a preferred embodiment of the thermoforming-shrink-wrapping process of the invention, the polyester film of the bottom web is heat-shrinkable, it is formed with a stretch ratio higher than 1.26, and the sealed package is finally heat-shrunk.

Preferably, the polyester film for thermoforming-shrink packaging has a percent free shrink in at least one of the LD or TD directions of at least 3%, more preferably at least 4%, prior to thermoforming. Preferably, the polyester film has a percent free shrink in both the LD and TD directions of at least 3%, more preferably at least 4%, prior to thermoforming as measured according to the test method described in this experimental section.

Preferably, the polyester film has a total percent free shrink of at least 5%, more preferably at least 10%, prior to thermoforming as measured according to the test method described in this experimental section.

Advantageously, the polyester film used in the thermoforming-shrinking process exhibits significant shrink properties after thermoforming, thus allowing tight shrinkage around the product and improved appearance of the package without wrinkles or voids after mild heating in, for example, an air-shrink tunnel.

In particular, the polyester film used in the thermoformed-shrink food packaging of the present invention has a percent free shrink in at least one of the LD or TD directions after thermoforming of at least 15%, more preferably at least 20%.

The polyester film used in the thermoforming-shrink food packaging process of the present invention exhibits a percent free shrink after thermoforming of at least 15%, more preferably at least 20%, even more preferably at least 23%, in both the LD direction and the TD direction.

The polyester film used in the thermoforming-shrink food packaging process of the present invention exhibits a total percent free shrink after thermoforming of at least 40%, preferably at least 43%, more preferably at least 45% or 50%.

The polyester film used in the packaging process of the present invention is preferably characterized by a tensile strength in at least one of the LD or TD direction measured at 23 ℃ (ASTM D882) of at least 1500 Kg/cm²More preferably at least 1600Kg/cm²。

The polyester film used in the packaging process of the present invention is preferably characterized by a tensile strength in both the LD direction and TD direction measured at 23 ℃ (ASTM D882) of at least 1500 Kg/cm²More preferably at least 1600Kg/cm²。

The polyester film used in the packaging process of the present invention is preferably characterized by an elongation at break in at least one of the LD or TD direction measured at 23 ℃ (ASTM D882) of at least 100%, more preferably at least 105%.

The polyester film used in the packaging method of the present invention is preferably characterized by an elongation at break measured at 23 ℃ (ASTM D882) in both the LD and TD directions of at least 100%, more preferably at least 105%.

The polyester film used in the packaging process of the present invention is preferably characterized by an elastic modulus in at least one of the LD or TD directions measured at 23 ℃ (ASTM D882) of at least 20,000 Kg/cm²More preferably at least 22,000 Kg/cm²。

The polyester film used in the packaging process of the present invention is preferably characterized by an elastic modulus measured at 23 ℃ (ASTM D882) in both the LD and TD directions of at least 20,000 Kg/cm²More preferably at least 22,000 Kg/cm²。

The polyester film for use in the present invention is dual bakeable so that the thermoformed container and package made therefrom can withstand reheating in a microwave oven or conventional oven and cooking with the package in a conventional oven at very high temperatures above 205 ℃ and up to 220 ℃.

The film of the present invention with peelable sealant provides an easy to open package. In addition, the films of the present invention provide a self-venting package, i.e., a package that opens at the seal and releases the internal vapor during cooking.

Due to the polyester-based composition, the films of the present invention provide final packages with excellent optical properties (transparency and gloss).

The polyester film for use in the present invention can be produced by any method known in the art for producing biaxially oriented films, for example, a tubular or flat film orientation method.

The polyester film, preferably the three-layer film, can be produced by coextrusion, by coating or by extrusion coating, preferably by coextrusion according to a tubular process or a flat process.

In the tubular process, also known as the "double bubble" process, simultaneous biaxial orientation is obtained by extruding a thermoplastic resin tube, which is subsequently quenched, reheated, then expanded by internal gas pressure to induce transverse orientation, and wound at a rate that will induce longitudinal orientation. An example of a device suitable for the described technique is disclosed in US 4841605.

In the flat film process, a film-forming thermoplastic resin is extruded through a T-die and rapidly quenched on a chill roll to ensure that the resin is quenched to an amorphous state. Orientation is then achieved by simultaneously or sequentially, preferably simultaneously, stretching the quenched extrudate at a temperature above the glass transition temperature of the thermoplastic resin.

In the continuous flat orientation process, the flat quenched extrudate is first oriented in one direction, typically the machine direction, i.e., the direction of advance through the film stretcher, and then in the transverse direction. The longitudinal stretching of the extrudate is conveniently carried out on a set of rotating rolls (MDO) rotating at different speeds. At least one of the first pair of rollers is heated, for example by internal circulation of hot oil. Transverse stretching is usually carried out in a tenter frame apparatus (TDO) comprising a number of heating devices and suitable stretching devices.

In simultaneous flat orientation, the resulting hot and sheared sheet is directed to the stretching zone of a simultaneous tenter. Any simultaneous stretching means may be used for the zones. Preferably, however, the clips are advanced by linear synchronous motors onto the entire opposing loops of the tenter frame. Bruckner GmbH has designed a suitable production line for simultaneous stretching with linear motor technology and is advertised as a LISIM production line. An alternative production line for simultaneously stretching extruded flat strips is the pantograph-based DMT line, which is equipped with two separate monorail on each side of the orientation unit. The configuration of the tenter can be varied depending on the desired draw ratio. In a subsequent annealing step, the biaxially oriented film may be dimensionally stabilized by heat treatment at a temperature below the melting temperature of the film.

Preferably, the polyester film used in the present invention is manufactured according to flat coextrusion. The polymer for the base layer b), the polymer for the heat-sealable outer layer a) and the polymer for the second outer layer c) are fed into separate extruders. The melt was extruded through a multilayer T-die and quenched on a chill roll. The casting so formed is then biaxially oriented, preferably simultaneously biaxially oriented.

In the case of sequential orientation, the longitudinal stretching (LD or longitudinal orientation) of the extrudate is suitably carried out in a temperature range of from 60 to 120 ℃, preferably from 70 to 100 ℃, and in the transverse stretching (transverse orientation) in a range of from 90 ℃ (preheating zone) to 130 ℃ (stretching zone), preferably from 90 ℃ (preheating zone) to 110 ℃ (stretching zone). The longitudinal draw ratio is in the range of 2.0:1 to 5.0:1, preferably in the range of 2.3:1 to 4.8: 1. The transverse draw ratio is generally in the range of 2.4:1 to 6.0:1, preferably in the range of 2.6:1 to 5.5: 1.

Preferably, however, the polyester films used in the present invention are simultaneously oriented.

The temperatures for simultaneous orientation are 90 to 110 ℃ (preheat zone) and 90 to 110 ℃ (stretch zone), respectively, preferably 90 to 100 ℃ and 93 to 103 ℃, respectively.

LD draw ratio from 2.5:1 to 5:1, preferably from 3.0:1 to 4.2:1, and TD draw ratio from 2.5:1 to 6:1, preferably from 3.2:1 to 4.4: 1.

The annealing is carried out at a temperature of 160 to 250 ℃, preferably 180 to 240 ℃, even more preferably 220 to 240 ℃. The annealing temperature can be used to fine tune the final shrink properties of the film.

Preferably, the polyester film used according to the invention is biaxially oriented and heat-set.

Preferably, the deep thermoformed polyester films used in the present invention have a percent free shrinkage on both LD and TD of less than 10% (measured in an oven at 180 ℃ over 5 minutes as described in the experimental section).

Preferably, the deep thermoformed biaxially oriented polyester film used in the present invention is heat-set to a total free shrink percentage of less than 15%, preferably less than 10% or 5%.

Preferably, the shrink-thermoformed biaxially oriented film used in the present invention has a total percent free shrink before thermoforming of at least 5%, more preferably at least 10%, as measured in an oven at 180 ℃ according to the test methods reported in the experimental section.

The biaxially oriented polyester film is finally cooled and wound up in a conventional manner.

Other methods of making the films of the present invention include coating the heat sealable polymer of layer a) onto a substrate layer comprising layers b) and c). Coating may be carried out using any suitable coating technique including gravure roll coating, reverse roll coating, dip coating, bead coating, extrusion coating, melt coating or electrostatic spraying. The coating may be performed "off-line", i.e., as a separate step after stretching and subsequent heat-setting of the base layer, or "on-line", i.e., before, during, or between any stretching operations.

Prior to application of the heat-sealable layer to the substrate, the exposed surface of the substrate may, if desired, be subjected to a chemical or physical surface modification treatment to improve the bond between the surface and the subsequently applied layer. For example, the exposed surface may be subjected to high voltage electrical stress that accompanies corona discharge. Alternatively, the exposed surface may be pretreated with a solvent or swelling agent known in the art, such as a halogenated phenol dissolved in a common organic solvent, for example a solution of p-chloro-m-cresol, 2, 4-dichlorophenol, 2,4, 5-or 2,4, 6-trichlorophenol or 4-chlororesorcinol in acetone or methanol.

The polyester film used in the present invention may be printed. Printing the material prior to thermoforming improves consumer appeal.

The top and bottom webs are preferably approved by the relevant authorities for food applications in view of the use.

The method according to the invention comprises the following steps:

-providing a thermoformable, dual bakeable biaxially oriented polyester film as described before as a base web;

-forming the bottom web so as to provide at least cavities having openings;

-placing a food product in the cavity through the opening;

-closing the cavity at the opening, preferably under vacuum, by hermetically sealing the bottom web to itself or by providing a dual ovenable top web and hermetically sealing the dual ovenable top web to the bottom web around the opening; and

-cutting out the sealed package.

The method for packaging thermoformed food of the present invention is characterized in that

-i) in the forming step, the draw ratio is higher than 1.26 (deep-drawing food packaging process), preferably higher than 2, higher than 3, higher than 4 or even higher than 4.5, to provide a deep-drawing thermoformed package, or

Ii) using a heat shrinkable film and carrying out a further final shrinking step after thermoforming (thermoforming-shrink food packaging process), thereby providing thermoformed-shrink packaging.

Preferably, the method of packaging thermoformed food products of the present invention is characterized in that

-i) in the forming step, the draw ratio is higher than 1.26 (deep-drawing food packaging process), and

ii) using a heat shrinkable film and carrying out a further final shrinking step after thermoforming (thermoforming-shrink food packaging process), thereby providing a deep drawn thermoformed-shrink package.

Preferably, the thermoformed cavity ends have a peripheral heat sealable flange around the opening.

If present, the top web can be any bi-bakeable film suitable for hermetically closing the openings of the cavities thermoformed in the bottom web.

The top web may be shrinkable or non-shrinkable, thermoformable or non-thermoformable, having the same or different, generally smaller thickness than the bottom web, depending on the desired final packaging variant.

The top web may be a flat film, another thermoformed flexible container (typically used for packaging protruding products), or a stretched film.

In one embodiment, the top web is a different film than the bottom web.

The dual ovenable top web may be a single layer film, preferably based on polyester, or in the alternative may be a multilayer film comprising a substrate, preferably based on polyester, and a heat sealable layer. The heat-sealable layer participates in the formation of a bond with the bottom web to provide the final hermetic package.

Since the bottom web includes a heat seal layer, the top web may or may not include a heat seal layer.

In one embodiment, the top web has the same composition as the bottom web.

In one embodiment, the top web has the same composition and thickness as the bottom web.

In one embodiment, the top web has the same composition, thickness and shrinkage properties as the bottom web.

In one embodiment, the top web is the same film as the bottom web.

The total thickness of the top web is typically from 12 to 200 microns, preferably from 12 to 100 microns, more preferably from 15 to 35 microns.

The forming step of the packaging method of the invention is a step of forming at least one cavity in the bottom web, said cavity preferably being surrounded by a flat peripheral portion, i.e. a flange.

The shaping step is carried out by thermoforming, preferably vacuum thermoforming, possibly plug assisted thermoforming, according to conventional techniques and using commercially available equipment.

"thermoforming" refers to a process comprising the steps of: the material is heated to a temperature (T1), where T1 is above the glass transition temperature (Tg) of the material, and if the material exhibits a crystalline melting temperature (Tm), where T1 is below the crystalline melting temperature, then the material is subjected to deformation, i.e., the material is deformed when it is in its softened, rubbery solid state.

In one embodiment, the packaging process of the present invention is carried out at a higher draw ratio (deep drawing) without any final shrinkage of the package.

In the deep-drawing food packaging method, the draw ratio in the forming step is preferably higher than 2.0, higher than 2.5, higher than 3.0, higher than 3.5, higher than 4.0 or even higher than 4.5.

The deep drawing method provides a great degree of freedom in the shape and size of the container. The film of the present invention allows for smooth and deep drawing, providing a container with uniform thickness, large internal volume and high die definition.

The step of closing the cavity requires heat sealing the top web to the bottom web around the opening, preferably along a dedicated flat surface, i.e. along a peripheral flange, or self sealing the bottom web at the cavity opening.

For effective heat sealing, the polymeric material of at least one heat sealable surface should soften to a degree sufficient to adhere to the other surface to be sealed.

Generally, the heat seal properties of a polyester layer having a melting temperature (Tm) develop at temperatures below Tm, and in this case, Tm does not have to be exceeded when forming a heat seal bond.

Exemplary heat seal temperatures for the top and bottom webs of the present invention are 190 ℃ to 220 ℃.

In another embodiment, the packaging process of the present invention is a thermoforming-shrink packaging process wherein at least the bottom web is heat-shrinkable, optionally both the top and bottom webs are heat-shrinkable.

The heat shrinkage of the packaging material of the bottom web or both the bottom and top webs caused by the heat treatment provides the desired tight appearance for the final preferred vacuum packaging.

The polyester film used as the bottom web in the thermoforming-shrink food packaging process of the present invention has a very high shrinkage after thermoforming, thus providing a very compact dual bakeable, preferably vacuum packaging without wrinkles and residual bubbles.

There are several variations of the thermoforming shrink-wrapping method of the present invention, such as the use of caps, which may or may not be heat shrinkable, may or may not be deep drawn, or may not be stretched over the product.

Furthermore, there are different ways in which the package can be shrunk, for example by heating only the deep-drawn container or the entire package, performing the heat-shrinking step on the final package leaving the seal, preferably a vacuum chamber, or performing the heat-shrinking step while the package is still in the vacuum chamber before or after the package is sealed.

Preferably after sealing, outside the seal, preferably outside the vacuum chamber, the shrinking is performed using an air shrink tunnel.

In fig. 3, a "thermoforming-shrink" packaging process is schematically illustrated. A film, indicated with 1, in the form of a web blank unwound from a roll and transversely clamped by an endless chain (not shown in the figures) and directed from the entrance of the production line to a deep-drawing station F. In the station, once the heating plate 101 has heated the film to a temperature sufficient to soften it, the softened thermoplastic film is deep drawn in the mold 100. Heating may be accomplished by radiation (e.g., infrared radiation), convection, conduction, or any combination of these methods. The temperature reached by the film should be high enough to shape it well, but not too high, or the film may flow excessively. Typically, temperatures of about 180-. In the basic molding process, the primary force bringing the softened plastic film into contact with the mold is the pressure difference between the two sides of the plastic sheet. This can be achieved by applying a vacuum through a port in the mold (at the bottom of the mold, not shown) and/or by forcing the softened plastic into contact with the mold by compressed air from the port (in a plate above the mold, not shown). Other methods, such as plug-assisted thermoforming methods, may be used in the forming step, but for films like the films of the present invention, it does not appear to be necessary to use these more complex methods. The mold may be a single or multi-cavity mold, and the shape of each cavity may be varied as desired. It is preferred to use a mold having a depth of about 40 to about 140 mm. Once the forming step in station F is completed, the moulds 100 are lowered and the formed containers 2, still joined together by the laterally gripped plastic web, are guided along the packaging line to a loading station G where they are loaded manually or automatically with the products 3 to be packaged. The loaded container is then moved to a vacuum sealing chamber H where the upper film 4 is supplied on top of the loaded container 5. The vacuum-tight chamber H is made of a lower part 102 and an upper part 103 which can be moved in a reciprocating manner in the direction of the arrow to close the chamber. Once the chamber is closed, the space within the chamber, including the space between the loaded deep-drawn container 5 and the upper membrane 4, is evacuated, and then a sealing frame (not shown in fig. 3) is actuated to seal both along the flanges of the deep-drawn container. If the product loaded into the deep-drawn container protrudes above the plane of the container flange, the upper film 4 will necessarily be deep-drawn like the lower film, or stretched over the top surface of the product. In both cases, the upper film will have to be held laterally by a multi-strand endless chain. In the former case, a forming station as described above but providing an inverted deep-drawn container would be present upstream of the vacuum sealing station H to deep-draw the upper lidding film. The mould used in this case will have the same shape as the mould for the lower film, but not necessarily the same depth, and the deep-drawn container 3 and the deep-drawn lid obtained from the upper film 4 will enter the vacuum sealing station H so that their flanges will overlap once the chamber is evacuated. In the latter case, the clamped upper film is heated to a degree sufficient to allow it to be easily stretched before being introduced into the vacuum-tight chamber. Heating may be achieved by contacting the film with a heating plate 104 or by any other known means.

Once the package is sealed in the vacuum-tight chamber H, air is restored into the chamber and the chamber is opened. The packs 6(I) are separated inside or outside the vacuum chamber by means of devices such as cutting knives and then conveyed to a shrinking station L where they are subjected to a heat treatment which shrinks the packaging material and gives the final pack 7 a tight appearance. A water bath, a hot air channel or an IR heater, for example, may be suitably employed in the step.

In one embodiment, the packaging process of the present invention comprises deep drawing of the bottom web and final shrinking of the closed package.

The deep draw thermoforming-shrink wrapping process may be summarized as including the steps of:

1. the biaxially oriented, heat-shrinkable bottom web which can be baked in a two-stage process (polyester film of the invention as described above) is heated and shaped in a mold with the aid of positive or negative pressure, so that the bottom web is shaped deeply in the shape of a deep mold.

2. The food product is placed in the forming cavity of the bottom web.

3. Preferably, the vacuum is applied and the top web is heat sealed to the openings of the cavities in the bottom web so that the package is completely sealed.

4. The entire package is heat shrunk to obtain a better and more attractive appearance.

In the thermoforming-shrink packaging process of the invention, the biaxially-oriented film that is dual-bakeable is heat-shrinkable and is characterized in that the% free shrink on at least one of LD or TD, measured as described in the experimental section before thermoforming, is at least 3%, preferably at least 4%.

In the thermoforming-shrink wrapping process of the present invention, the biaxially-oriented film which is bakeable after thermoforming is characterized by a total free shrink percentage of at least 40%, preferably at least 43%, more preferably at least 45% or 50%, measured after thermoforming as described in the experimental section.

A second object according to the invention is a dual bakeable thermoformed flexible container comprising a thermoformed cavity and an opening, made by thermoforming a film of the above-mentioned bottom web, wherein the thermoformed cavity has a depth of more than 1 cm and/or the thermoformed container is heat shrinkable.

The flexible container according to the invention has a stretch ratio higher than 1.26, preferably higher than 2.0, more preferably higher than 2.5, even more preferably higher than 3.

Preferably, the thermoformed cavity has a depth of greater than 2 cm, more preferably greater than 3 cm, or 4 cm, or 5 cm, or 6cm, or 7cm, or 8 cm, or 9 cm, or 10 cm.

Preferably, the thermoformed containers of the present invention are heat shrinkable. In particular, the thermoformed film of the container has a total free shrinkage percentage, measured as described in the experimental section after thermoforming, of at least 40%, preferably at least 43%, more preferably at least 45% or 50%.

Preferably, the container of the present invention is both deep drawn, i.e. thermoformed at a depth of above 3 cm, or 4 cm, or 5 cm, or 6cm, or 7cm, or 8 cm, or 9 cm, or 10 cm, and heat shrinkable, i.e. has a total free shrink percentage after thermoforming of at least 40%, preferably at least 43%, more preferably at least 45% or 50%.

Preferably, the container comprises a cavity, an opening and a flat surface (i.e. a flange) surrounding the opening, onto which the top web can subsequently be sealed, thereby providing an air-tight flexible package.

From the deep-drawing tests described in example 1, it can be seen that the thermoformed container according to the invention is characterized by a uniform thickness of thermoformed film along the bottom and in particular along the walls, which is not possible with the comparison of the prior art films Mylar. This uniform distribution of material after thermoforming is attributed to the high formability of the film used to make the container of the present invention.

Preferably, in the container of the invention, the thickness of the film, measured at the bottom of the container after thermoforming, is less than 25 microns, more preferably less than 20 microns, even more preferably less than 15 microns.

In one embodiment, the thermoformed container may be prepared by thermoforming a composite comprising a polyester film as described previously adhered as a liner to a paperboard by conventional techniques, for example by glue lamination or thermal lamination.

Fig. 1 shows a cross-section of a deep-drawn thermoformed container (201) according to the invention. The container (201) may be part of a semi-finished web comprising a plurality of thermoformed containers (201). Each container (201) comprises a drawn part forming a cavity (202) defined by a bottom (202a), a side wall (202b) projecting from the bottom and a top opening (203) (see dashed lines in fig. 1).

The top opening 203 is surrounded by a flat peripheral portion 204 (i.e., a flange). The top opening (203) forms an inlet mouth through which the food product to be packaged is introduced during the packaging process. When viewed from the top, the opening (203) may take any convenient shape, such as rectangular, square, circular, oval, or other shape suitable for allowing product to enter the cavity (202). The container (201) is characterized by a height H, a length L, and a width W.

As previously mentioned, the actual stretch ratio may be calculated based on the measurements of the cavity of the thermoformed container (H, L and W).

The difference in the calculated stretch ratio for the mold and the actual stretch ratio calculated for the thermoformed container may provide an index of the actual formability of the film. However, the evaluation is difficult if the thermoformed container has an irregular shape or does not have a flat surface.

As explained in detail in the experimental section, a simpler formability index: (Shrinkage index after thermoforming) It can be indirectly calculated from the volume of the thermoformed cavity of the container and the mould, evaluated by weighing the water required to fill said volume.

Preferably, the polyester film used in the process of the present invention and the containers made therefrom have a shrinkage index after thermoforming, measured as described in the experimental section, of less than-35%, more preferably less than-30%, even more preferably less than-25% or-20%.

Advantageously, the thermoformed container of the present invention is then used to package an article (food product), preferably vacuum sealed, and preferably shrunk, thereby providing a tight package.

A third object according to the invention is a dual ovenable, air tight thermoformed package comprising

A dual ovenable, thermoformed, flexible container, as previously described, comprising a thermoformed cavity and an opening,

a food item to be placed in the cavity,

the opening is hermetically closed by a flexible container that is self-sealing at the opening or by a dual bakeable top web sealed to the container around the opening.

In one embodiment, the package according to the invention does not comprise a top web, but only a flexible container which is self-sealing at the opening of the cavity, thereby enclosing the product.

Preferably, the package according to the invention comprises a top web sealed around the opening of the container.

With regard to possible variants of the packaging according to the invention, the same possibilities as reported for the packaging method apply here, i.e. the presence or absence of a top web, a flat, stretched or stretched top web, a heat-set or heat-shrinkable top web, etc.

In the thermoformed packaging according to the invention, preferably deep-drawn and/or shrunk packaging, at least the container according to the invention is thermoformed.

In this case, the opening of the container may be closed by a non-thermoformed lid, which may be made of the same film of the container or of a different dual-bakeable film.

In one embodiment, the non-thermoformed lid and thermoformed container are made from the same film as described above. Preferably, the film of the lid is thinner than the film of the container.

In another embodiment, both the top and bottom of the package may be thermoformed at the same or different depths, but at least one of them is deep drawn.

Preferably, the package of the present invention is evacuated.

Preferably, the package of the present invention is evacuated and heat shrunk.

Thermoformed packages are typically obtained on a thermoforming machine that uses a web of material. Two rollers are used, one for the bottom web, which is unwound, heated by a hot plate and forms the cavity in which the product to be packaged is subsequently loaded, and one for the top web, which, if present, is sealed to the bottom web inside a sealed vacuum chamber, from which air has preferably been removed.

In one embodiment of the present package, the bottom portion is thermoformed to provide a cavity and a peripheral flange, and the top portion is sealed around the flange. The thermoformed base can be preformed or thermoformed in-line, preferably it is thermoformed in-line.

In one embodiment of the present package, the package comprises two separate sheets of film: top and bottom portions sealed together along a peripheral surface around the product. In the embodiment in which the base is thermoformed, thus providing a cavity, the top and base films are both dual ovenable films made substantially of polyester as defined above, preferably the top and base films are the same film, more preferably both are heat shrinkable.

In the package according to the invention, the product is a food product, preferably a food product selected from the group consisting of fish (whole or in small portions), meat, in particular fresh red meat, processed meat, poultry, pork, lamb, baked goods (also partially baked or frozen), seafood, stabilized vegetables or ready-to-eat meals.

Optionally, the packaged food product may be frozen for longer storage, and then the same package may be placed directly in an oven for cooking.

In a preferred embodiment, the package according to the invention is self-venting, i.e. it allows excess steam to escape the package during cooking. Advantageously, during cooking, the opening of the package of the present invention along the seal is limited, thus preserving a portion of the juices and thus providing a well cooked food that is palatable, tender and juicy inside the food, yet surface toasted.

Therefore, a fourth object of the present invention is a method for cooking a food product comprising

-providing a dual ovenable thermoformed package according to the invention comprising said product, and

-cooking the packaged food product in the package in a microwave oven or a conventional oven.

In one embodiment of the method, the cooking step is performed in a conventional oven at a temperature above 205 ℃ and/or up to 220 ℃.

Examples

The invention may be further understood by reference to the following examples, which are illustrative only and should not be construed as limiting the scope of the invention as defined by the appended claims.

The film used in the method of the invention comprises the following resins:

PET1: RAMPOT N180, an Indoma polyester, a copolymer of terephthalic acid, isophthalic acid and monoethylene glycol, a density of 1.4 g/cc, an intrinsic viscosity of 0.80 dl/g, a glass transition temperature of 78 ℃, a melting point of 245 ℃.

PET2: copolyester Eastman Chemical EASTAPAK 9921, density 1.4 g/cc, melting point 238.0 deg.C, intrinsic viscosity 0.80 dl/g.

PETG1: copolyester of terephthalic acid, 1, 4-cyclohexanedimethanol and ethylene glycol, EASTAR PETG 6763-Eastman Chemical, polyethylene terephthalate/glycol, density 1.27 g/cc, glass transition temperature 81 ℃, melt flow Rate (C)ond.200 deg.C/05.00 kg (G)) 2.8 g/10 min, viscous solution 0.75 mPa.sec.

PETG2: an antiblock and slip masterbatch of amorphous polyethylene terephthalate/glycol, a copolyester of terephthalic acid, 1, 4-cyclohexanedimethanol and ethylene glycol, SUKANO G dc S503 silica 10%, wax 6%, bulk (apparent) density 1.2G/cc, Vicat softening point 82 ℃.

Modified LLDPE: BYNEL 4104 (2006) DuPont, maleic anhydride modified ethylene/butene copolymer, density 0.9200 g/cc, melt flow rate (Cond. 190 ℃/02.16 kg (E)) 1.10 g/10 min, melting point 125 ℃.

EAA: PRIMACOR 3440 Dow ethylene/acrylic acid copolymer with comonomer content acrylic acid 9.7%, density 0.938 g/cc, melt flow rate 190 ℃/02.16 kg 10 g/10 min, Vicat softening point 76 ℃.

In tables 1 and 2 below, the compositions (in% by weight relative to the weight of the layers) of the films 1 to 9 used in the thermoforming process according to the invention are shown:

TABLE 1

TABLE 2

Films 1 to 9 were manufactured in a tenter LISIM @ production line according to the following method and conditions.

The three layers were coextruded through a three layer feedblock and then distributed through a flat die with a multi-manifold system. Quenching the melt from the die onto a cooling roll; electrostatic pinning is used to facilitate intimate contact between the melt and the chill roll. The casting so formed is then biaxially oriented.

Stretching was performed simultaneously at an orientation ratio of 3.6:1 in the MD and 3.8:1 in the TD, and at temperatures of 95 ℃ (preheat zone) and 98 ℃ (stretch zone). The film is annealed at a temperature of 230 ℃ to 235 ℃ before exiting the oven. Finally the biaxially oriented film was cooled, edge trimmed and wound into a roll (mill log).

Comparison film

Mylar OL is a dual bakeable biaxially oriented polyester film with a heat seal layer of amorphous polyester, produced by DuPont Teijin, commercially available at nominal thicknesses of 50, 75, 100 and 150 microns. There is no information about the polyester of the base layer.

Mylar CKP5E is an uncoated formable polyester film designed by DuPont Teijin for shallow draw thermoformed two-way bakeable packaging, also known as Mylar COOK, designed for use in most web thermoforming equipment. Polyester is defined as a polyethylene terephthalate polymer.

Test method

The films used in the thermoforming process of the invention and the commercial comparative films were evaluated using the following test methods:

free shrinkage%: evaluations were made both before and after thermoforming, as explained below.

Free shrinkage before thermoforming%: a 12 cm x 12 cm square sample was cut from the film tested. On the surface of each sample, a 10 cm x 10 cm central square was drawn with a pencil.

The samples were placed in a laboratory oven for 5 minutes at 180 ℃ in air without restriction. The dimensional change of the outlined squares for each sample was measured in both LD and TD.

For each of the LD direction and the TD direction, the percent free shrinkage is calculated by the following formula

[(Lo -Lf)/Lo]x 100

Where Lo is the initial length (mm) of the film sample before testing and Lf is the length (mm) of the film sample after shrinking.

Total free shrinkage%: which is the sum of the% free shrinkage on LD and TD of the film samples measured as described above.

Free shrinkage after thermoforming%: a 7cm x 7cm square sample was cut from the bottom of the thermoformed material under test. On the surface of each sample, a middle of 5 cm x5 cm is drawn with a pencilA heart square.

The samples were placed in a laboratory oven for 5 minutes at 180 ℃ in air without restriction. The dimensional change of the outlined squares of each sample was measured in both the LD direction and the TD direction.

For each of the LD direction and the TD direction, the percent free shrinkage is calculated by the following formula

[(Lo -Lf)/Lo]x 100

Where Lo is the initial length (mm) of the film sample before testing and Lf is the length (mm) of the film sample after shrinking.

Maximum contraction tension: that is, the force per original unit width produced by the film in the machine direction (LD) or Transverse Direction (TD) as the film attempts to shrink (while under restraint) at a particular temperature is measured by the following internal test method: a 25.4 mm wide strip of film was cut from the sample in either the machine direction or the cross direction. The force measurement is carried out by means of a load cell to which the clamping jaws are connected. Opposite to the clamping jaw, a second clamping jaw with the sample fixed thereto is adjusted to a suitable position by means of an external handle for pre-tensioning the sample. Two clamping jaws hold the sample in the center of the channel into which the impeller blows hot air. Three thermocouples were fixed in the air passage to measure the temperature. The temperature of the sample as measured by the thermocouple was raised to about 180 ℃ at a rate of about 2 ℃/sec and the force was measured continuously. The measured force was then divided by the original width of the sample to obtain the shrink force, and further divided by the thickness of the film sample to obtain the shrink tension. Typically, the shrink tension is in kg/cm²And (4) showing.

Modulus of elasticity:(23℃) ASTM D882

tensile strength and elongation at break:(23℃) ASTM D882

haze degree：ASTM D1003

Gloss:ASTM D2457 (60°)

tg and melting Point:ASTM D3418

formability of: by visual inspection, by finding defects in the material conforming to the shape and detail of the mould, by measuring the thickness of the material in different parts of the thermoformed container and by rootThe formability of the film was evaluated by evaluating the volume of the cavity according to the volume test described below.

Volume test (shrinkage index after thermoforming)

The purpose of this very simple test is to evaluate the formability of the film and its shrinkage after thermoforming by measuring the actual volume of the cavity of a container made of the film by thermoforming under specific conditions. The volume of the cavity of the thermoformed container was evaluated indirectly by measuring the weight of water required to fill the thermoformed cavity up to the flange. The higher the weight of water, the larger the volume of the cavity and, therefore, the more formable the film.

Thus, considering a water density of 1 g/cc, the volume difference of the thermoformed cavity and the mold in percent can be calculated as follows:

Δ V% = [ (V cavity-V mold)/V mold ] x 100= [ (Ww cavity-Ww mold)/Ww mold ] x 100

Where V is the volume in cc and ww is the weight of water filled in the cavity or mold in grams.

The greater the formability of the material, starting from the same mould and under the same thermoforming conditions, the more the difference in percentage by volume tends to be 0%, since the volume of the cavity tends towards the volume of the mould.

The dimensions were measured by using a T200MULTIVAC machine (hot plate above the forming station, heating temperature 190 ℃, heating time: 2.5 seconds, forming time: 2 seconds): the tests were carried out with a 135 mm x 180 mm x50 mm die thermoforming the material at a depth of 50 mm.

The test is particularly suitable for comparison purposes, since for fixed mould and thermoforming conditions it allows to compare the actual formability of different materials simply by weighing the respective thermoformed containers filled with water.

Film Properties

The shrinkage, mechanical and optical properties of the films used in the process of the invention are collected in table 3 below:

TABLE 3

These properties were measured according to the methods described above.

The percent free shrink and maximum shrink tension of film 7 before and after thermoforming and a commercial comparative thermoformable film (MylarCKP5E) were evaluated using the previously reported test methods and are collected in table 4 below:

TABLE 4

Thermoforming was carried out on a T200MULTIVAC machine equipped with dies of dimensions 135 mm x 180 mm x50 mm under the following operating conditions: heating temperature of 180 ℃, heating time: 1.5 seconds, molding time: 1.5 seconds.

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Use of a dual bakeable polyester film in thermoformed packaging applications and dual bakeable thermoformed packages obtained therefrom

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